I gave in and took my prime out for inspection. In short, yeh its not the best quality, but the paintwork is no worse than most other MP4's i've seen. I had to fiddle around quite a bit to get things to work/fit properly (my chest panel wouldn't close properly when I transformed him back to robot but I figured out how to lock it in properly).
My only REAL gripe is the leg shortening mechansim on prime's left leg. It took a bit of fiddling to even get it to work and it's still a little loose so prime stands about a mm shorter on that leg. I don't mind visual defects but mechanical ones suck. (EDIT: I've since taken apart prime's leg and fixed the defect with a little electrical tape)
If I had problems like a missing wheel I definitely would have returned it too.