The reasons paint will crack, flake, or peal on a bumper is generally due to the prep and "ingredients" that were used in the re-paint job.
Due to the ability of the bumper to flex upon impact the paint needs to have a certain amount of urethane added in the right amount to the paint. I am not an expert, but have been told that it is not as easy to do this correctly and is more expensive than painting other parts of the body.
Bottom line is a real expert in painting and body work will know how to do this - a shop using a "quick and dirty" method won't get it right. Both ways will look the same but the difference will show the next time you get tapped.
I hate to say this but I've always made sure that I know shops in advance who are excellent and have their number ready....just in case, rather than waiting til I need to know.
I'm sure the real experts can give a more detailed answer or correct me.
"As ye sow, so shall ye reap" - Me
Mine at sunset