Back camera lens scratches

As long as the scratches are minor, it tends to have little to no impact on the photo and can usually be something you live with. Actual cameras (and lenses) are the same; if it's minor, it probably doesn't matter but it usually results in a good discount if you can tell it doesn't matter, or can test it and see it has no impact on the final result.

However, you do want to be more careful going forward because anything deep DOES tend to show. I'm not even kidding; I can take home a high-end Canon EF L lens with a scratch in an area it means absolutely nothing with a blemish I can tell will not cause issues (and just put a filter on it in the field); but as a general rule, I want to test those where I can see for myself it doesn't matter first, or make sure the price to risk ratio is good enough I'm comfortable with gambling a bit. However, these need to be tested before any shoot you cannot take chances on; put some shots on them throughout the day and night, even a few risky shots like sunset times. There's a reason we use "UV filters" to protect lenses and the ones which do not get them are either cheap, or as common as a lot of trading cards where it doesn't matter. (Ex: Kit lenses (18-55/Sony 16-50, many others), EF-S lenses (WILL NOT WORK on full frame bodies, which is why) and common APS-C only Nikon DX; not common, but if it's notably only friendly with APS-C bodies it isn't going to be expensive as people dump them on the used market a lot more). Other times the cost to replace it is less than a filter will cost, unless it's an excellent copy. I'm not spending $20-30 on a filter for a subpar but good copy of a common lens which isn't much more to find a better copy of if I needed to but if I had one, fine.
The other group of lenses which get chanced are "disposable" lenses; think EF-S 18-55 IS/IS II, Nikon's 18-55, and the Sony 16-50 E-Mount lens a lot of copies are available used due to lens bundles and the a5000 giving every buyer a copy so they sell the a6000 and up as "body only" knowing we will just use the one from the a5000. Granted the 18-55 STM is less disposable, but it's still an 18-55; if I break it I can PROBABLY replace it pretty easily so I'm not going to be extra cautious. They are so easy to find that if I broke one all I need to do is either buy a good used copy on its own for $50-60, or a used body that comes with one or two of them (if I'm in the market and it's not overly used). The owner of the lens can keep the thing; they're so common, I can get another copy all day long so if you broke one of mine I'm pocketing the money.

However, I would say the vast majority of lenses we gamble on are common collectibles with near zero resale like Canon EF-S 18-55 IS/IS II since Canon shoves them down your throat on entry-level bodies; and sellers without lens caps just throw one on the camera when you're selling a used prosumer camera and throw an extra $50 on the price -- again, like the manufacturer they know what we think of them, but they keep the markdown low on purpose so we don't argue about it. There's a reason they use the 18-55 STM on the prosumer side at least new; it's the only way we will not laugh at you. You're just peddling slightly less trashy kit lenses at that point so that's why places like Best Buy make you buy that version or stock more than body only (profit margins). On the other hand, Canon pretty much expects anyone buying a prosumer EF/RF camera to own lenses and lets you pick; save $150 and put it towards accessories, or buy a better lens if you need something.

Either way, I think the 18-55 and deals on pointless blemishes make my point clear... If it doesn't affect things be more careful next time. For cameras, test it and if it doesn't matter, snatch it up and put a few test shoots on it before fully trusting it.