SRV1981

I wouldn’t even be slightly concerned about any such minor discrepancies.
Yes, there is getting it right in camera, ie, technique (including lighting) and there is bound to be some fiddling in post to ‘equalise’ the output between any combo of bodies and lenses etc.
Just bring some drone footage into the mix and there’s something else to ‘equalize’.
I’d be far more concerned with how the tools feel to work with; weight, ergos etc.
Sony, Nikon, Lumix, Canon…it’s not difficult to match it, never mind keeping it in brand.
Unless you tell folks or ask, no one ever knows what you shot it on.
And outside of nerds like us, no one cares!

If you prefer the 'look' from a particular camera, then I guess you should buy that one...
But as soon as you take it outdoors under a broken cloudy sky and press the record button, the angle, intensity and colour of the ambient light will be constantly changing, giving you an ever changing palette of 'looks' that you didn't ask for... which as Kye suggested above you'll have to adjust for in post anyway to get a cohesive 'look'.
(I was once on the top of a mountain pass, looking down a wide valley, in the aftermath of a storm the day before. The fast moving thick clouds meant it would change from bright sunshine to deep shadow every few seconds. It produced very dramatic lighting - and some nice stills and video - but setting camera exposure settings was almost a lottery...)

But objects in the footage from both cameras are the same size. If one camera is APS-C and the other is full-frame, and they were using the same lenses, those objects would not be the same size. So maybe the differences you're seeing are due to different lenses being used (or the same zoom lens on both cameras but at different focal lengths), or something was done in post. The person who did this comparison is introducing too many variables for it to be an informative test.

Without watching the videos and just looking at the screenshots, it looks like the ZV-E1 was exposed about 2/3 stop brighter than the FX30.  Assuming that it's 10-bit footage with a decent codec, you will drag a single slider slightly to the right in post and the images will look much more similar.
It is likely that the ZV-E1 has slightly more DR than the FX30 (full frame vs aps-c of a similar generation).  In the relatively low-contrast scene that's shown, if the exposure is within a stop or so of (what I think of as) correct, you would never know or care.

We all know that cameras produce (sometimes dramatically) different images and image quality, and yet we also know that within a given price range those same cameras typically use the same sensors from Sony and are recording to the same codecs in basically the same bitrates.  It's maddening!
So, WTF is going on?  
Well, I just came upon this talk below, which goes through and demonstrates some of the inner workings in greater detail than I had previously seen:
It's long, but here's my notes...
Firstly, how you de-mosaic / de-bayer the image really matters, with some algorithms being higher quality and require higher processing power:
(Click on the images to zoom in - quality isn't the best but the effects are visible)


If you're not shooting RAW then this will be done in-camera, and if your manufacturer skimped on the processor they put in there, this will be happening to your footage.
If the camera is scaling the image, then the quality of this matters too:

and if the scaling even gets done in the wrong colour space then it can really screw things up:

There's more discussions in there, especially around colour science which has been discussed to death, but I thought these might be illuminating as it's not something we get to see that much because it's buried in the camera and typically it's not something we can easily play with in the NLE.
All these add up to a fundamental principle that I have been gradually gravitating towards.
If you're shooting non-RAW then shoot in the highest resolution you can shoot in, and just un-sharpen (blur) the image in post.
Shooting in the highest resolution means that your camera will be doing the least downscaling (or none), and most glitches and bad processing will be at the pixel-level, which means that the higher the resolution the smaller those glitches and errors compared to the size of the image, and un-sharpening de-emphasises these in the footage.  
You might notice that all of these shortcomings make the footage sharper, not duller, so the errors have made your footage sharp but in a way that it never was - it's fictional sharpness.
Also, the more modern displays are also themselves becoming sharper, so it's no wonder that footage all now looks like those glitch websites from the late 90s that were trying to be cool but looked like a graphic designer threw up into them...

FilmLight (who make BaseLight which is the Resolve competitor that costs as much as a house) seem to be on a mission to get deeper into the image and bring along the industry on that journey, and I'm really appreciative of their efforts as they're providing more insight into things we can do to get better images and get more value from our limited budgets.

Those are all absolutely KILLER deals...  well done!!

I buy used all the time. Greatest deal were two LX10, a bit bumped up but perfectly usuable, for 120 Euro, three years ago, from a youtuber with 150.000 subs. One battery only though.:) Another great deal was an og pocket two years ago or so, with the 20mm 1.7 MK II for 200 or 250 Euro. Last summer I got a Lumix G2 and a G3, together for less than 30 Euro. This year no purchase yet, as planned to stay away from gas this year and as stated in another thread.:)

My mileage has not varied from this.
I think once, max twice in about the same time period so for me, extended warranties would have cost 10x if not 20x as much.
Otherwise I do try and purchase used if I can, but only from dealers ie, not places like eBay. Unless it’s some older ‘vintage’ lens type stuff when OK, I have taken a punt.
MPB is the only real place in Europe for used (mainstream) kit.

B&H, Adorama & MPB have all served me well when buying used. I bought my S5iix new, but that was because it was on sale and the used price wasn't much lower. If it's only $100 or $200 cheaper then it really might be worth getting it new instead, but I generally buy cameras that are a couple years old which is where you'll find bargains. 
You're probably going to get the same overheating on a used camera as you will on a new one, assuming the camera you're getting has overheating issues to begin with. The same applies for most issues a camera may have. 
Third party warranties aren't a terrible idea. I get extended warranties if they're available for any expensive purchase I make. For me that's usually anything over $1000, though what is and isn't expensive varies per person. I film a lot of pro-wrestling, so the thought of having my brand new $2,000 camera and $1,000+ lens damaged and being SOL because I didn't spend a little more on the extended warranty gives me nightmares. Better to be safe than sorry, I say. 

I've had some great bits of luck recently by using search terms that reflect what a person who didn't know what they had would use as a listing title - 'camera light' and so on... then sorting by Ending Soonest.

I'd try a range of things, and I'm sure others will have more to add, but I would:
Check the camera physically to make sure the screen works, buttons, EVF, etc I'd update the firmware straight away to the latest Put on several lenses and test that they're recognised correctly and the AF and OIS are working After putting in a new battery and formatting a memory card in it, I'd pick the best quality normal mode (24/25/30p) and do a long recording on it of something that has a lot of movement in it (a great test is putting three still images on a timeline each at 1 frame and then loop the video)..  if it records without issue for 20+ minutes without anything odd happening that's good, but if you have time I'd test until the card fills up or the battery dies I'd also do the same but on the highest frame rate mode Check the files are playable in the camera and work on the computer If it passes all of the above then it's unlikely that it has some lingering issue that isn't also present on new copies as well.

B&H and Adorama are my most trusted vendors for used stuff. Fun thing about Adorama is that almost all their used stuff on their site is also listed in their eBay store with a “Make offer” option so you’re able to buy things under list price. They’re pretty good about actually accepting offers, too. 

I’ve had very good luck buying and selling with MPB in the past, but you need to reallyyyy stress test stuff from them IMO. I’ve returned a couple items that I didn’t feel were listed correctly. Like, things I bought at “Excellent” that I would characterize as “Poor” or “Acceptable”. Still, there are some great deals there.

Aside from launch day preorders like the BMPCC4K, I buy almost all my cameras used from major retailers. You’d be amazed how many cameras get returned just a couple weeks after launch. Like new condition for 10-15% off. I stress test them quickly just to make sure there isn’t some defect. 
Typically, anything rated 9 or higher from B&H is indistinguishable from brand new.

 

About half my cameras were second hand, with a couple of them likely having a lot more than two previous owners, but haven't had any issues with mine.
If you're concerned about overheating, get a camera with a fan.  A fan is the difference between a camera overheating in air-conditioning in under 45 minutes vs a camera recording for 24 hours in a race car at 120F / 48C.

I've purchased some new and some used. If you're super lucky, you can buy new for used prices. IMO, that is the time to buy. For Panasonic, it's during Black Friday. A few years back, I got the Olympus E-P7 with the kit lens and the Olympus 75mm f/1.8 for 899 euros. That's probably the best deal I've ever found for new. In France, you have leboncoin, which is very good too with some amazing deals from people who just want to unload material or just don't understand what they have. When you buy, you have the choice of sending it back. If you know your cameras, you can thoroughly test it. Buying off Ebay is an option too, but you never seem to find good deals anymore (I gave up). MBP is also a great choice, but they're too expensive for some cameras and lenses.

If you are really worried about that, buy it and stress-test it quickly so that you can return ASAP it if you're not happy.
But if long recording times in hot environments are important to you, then you should be looking at a camera with a fan anyway (so you don't get distracted from the enjoyable creative stuff by worrying about overheating). Otherwise avoid leaving the camera out in hot direct sun/put a sunshade over it/put a white or reflective cloth over it. And turn it off when not using it, so it's not already hot before you press the record button.

I've owned many cameras (too many) and i think I've only ever bought 2 from new. Thing is, there are so few moving parts on cameras these days that there's not a huge amount that can go wrong in normal use. That said, unless an eBay or similar deal is just too good to pass up, you are safer doing it through a dealer, as @ac6000cw says.

If you want to minimise the risk buying used, buy the body from a major dealer who will provide a decent length warranty and allow you to return it if you're not happy with it e.g. in the UK, Wex offer a 45-day return period and provide 12-month warranties on used gear. MPB offer 6-month used warranties, as do some of the other major UK dealers.
If you want long warranties, buy new and then buy an extended warranty from the manufacturer, or wait until the manufacturer offers a free extended warranty as a sales promotion on new bodies.

I also buy most of my gear used; I did buy my Sony A7iii new, mainly for the warranty. For Blackmagic Design cameras I think it's best to buy used because BMD's quality assurance is so poor that you may need to buy several new cameras to find one that works. The two BMD cameras I bought new were defective out of the box and had to be returned; the used one I bought on eBay is perfect. People who buy a defective camera will likely return it to exchange, so you'll probably have better luck buying a used one.

according to my experience, this is true. 

Another thought and that is have you considered a full frame lens?
I wasn’t going to, but testing the photo side of my kit on 2x portrait shoots, I decided I did have a hole in my lineup...so bought another Tamron E Mount lens, the current version of the 28-75mm f2.8
Now I suspect in FF flavour you are going to call that too short, but on your APSC camera, it’s going to be a 42-112/3 equivalent.
Still too short, IDK, only you can answer that, but it weighs basically the same as the APSC 17-70, so thought it was worth mentioning?
 
 

Would easily be my first choice for APSC with a real world 28-105mm focal length and constant f2.8 aperture.

I just bought the Sigma 18-50mm f/2.8 for my Fujifilm, but it's also available in E-Mount.
I'd rather sacrifice some range and have a smaller lens.
Else there is also the Tamron 17-70mm f/2.8

I had the 18-135mm for a bit. It's a very compact and lightweight lens. Good range. Great AF. The weakness is obviously the f/5.6 aperture on the long end. It's fine for outdoors stuff, but I found myself really wishing I had an extra stop of light pretty consistently indoors. On my full frame cams, the 24-105mm f/4 is my workhorse. It strikes the right balance of range, aperture, and performance. I'd imagine the 18-105mm would be a similar experience on APS-C.

I agree the 18-105 is a really versatile lens: power zoom and near par focal. A little deficient on the wide end, but now there is a perfect complement: the Sony E PZ 10-20mm constant f4.
Shooting Sony APS-C has real advantages in terms of video-advantaged lenses.