Could have just been the owners idea of a mod as maybe he/she thought it looked better that way.
If you think it's been in a bump or something then you just need to do the normal used car checks ~ look for over spray, masking lines, colour mismatch, check shut lines, make sure things line up etc etc.
These cars are prone to stone chips though don't forget so it could just be that the bumper was resprayed in order to repair stone chips etc.