If it's a iPhone 4, they could have a scuffed lens.
I used to carry my phone without a case. I didn't really care if the back was scratched, it's a phone. I had a product similar to Invisible Shield on the front to keep the front looking good but the back was bare.
One of Apple's weird design flaws is that the camera lens sticks out like ever-so-slightly and when the phone is placed on the back, it's the part of the phone that makes contact. As a result, the thing takes a beating.
After about 6 months, the camera in the phone was useless. The lens had become so scratched that every single photo was blurred and had a halo effect to it. I didn't really care because I never take photos for any sort of remembrance purposes. Sometimes I photo funny stuff and send it to people as a text but that's about it.
Took it to the Apple store and they replaced the back. Cost me $25-$30, I think. Only did it because I found a case for it that is incredibly thin. Almost like it isn't even there at all, thin. Made by elago (I think it's probably the best case I've ever had. It's not gonna protect it like an OtterBox will but it's so small that it's unnoticeable and that's all I care about). Anyway, found a case and figured I might as well get the back replaced if I am going to case the thing up.
Here's a picture I took from the phone after a thunderstorm in Kansas a few years ago.
Here's another picture I took when I still had the case on it. Toured the Coors factory and afterward a buddy of mine wanted to hunt down "The 7 Minute Pour". I think it's called Barmen. Literally takes like 7 minutes to pour a glass because the head builds up so much.
I think they look good. Certainly not going to win any awards with it but good enough for what I use it for.
But, then the case came off and things went to hell.
Here's one I texted to a friend of mine who loves this beer. Probably 9 months after having the phone, only a couple months after I quit using a case. If you know anything about this beer, you'd know that a lemon shouldn't even be near it. I had this beer for the first time in Brussels after getting laughed at for pronouncing the name wrong. They probably would have asked me to leave had I asked for a lemon. Felt a little let down when a place that advertises it's own beer brought the lemon with the beer.
You can see the beginning of the end. Upper left corner just looks blurry. It progressively got worse and eventually the whole picture would be hazy like that.
It's a phone so I don't know what people expect from the beginning. Certainly I think the pictures I took before taking the case off look good. I guess If I wanted anything more I'd probably look into making photography a hobby and purchase a device made specifically for taking pictures. Some of the cameras out there are pretty nuts. I was at a family gathering not too long ago and one of my relatives is big into photography. He brought two cameras with him to show a couple of my younger relatives some options they could go for if they wanted to get serious about photography. He's toting around this camera with what looks like the Hubble Telescope hanging off it. I joked with him a bit and then he pulled out some of the pictures he has. Unreal. Live action still shots of some sort of stage production his daughter was in, from half the room's distance away and in dark lighting. Said he didn't really adjust for much, just snapped it. The picture was unreal and he zoomed in like 500% before it started to appear even the slightest bit grainy. I was impressed for a few seconds.
Long story short, have them check the lens for scuffing if the photo looks hazy or blurry.