This happens a lot, It is just because users aren't as versed in photography as we are and they think that we can turn their Low resolution images into high resolution images. There isn't much we can do. People also tend to not rate at all, I think they need to make both like big pop ups on your screen once they receive an edit in order to request your next edit.
For the Record, if you don't know what flagging is - There is a flag on the bottom of each thumbnail, and if you believe the photo is too low res, or if somebody is asking for something that isn't possible etc, you can press the flag and give a reason, then flag. If two of us do this it will disappear from the photo pool and the guys at Mendr will contact the user and tell them that they can't do it. This includes if they request more than what they paid for too, something they request a lot and it's only labeled as an editors touch. A lot of time people just don't know how to request more though.
I think it will just take time for users to get used to the app and if we have suggestions for improvements, the team at mendr always appreciates them. So let them know!