just had a fibre glass bumper painted up for my car and its only been on there 3weeks and the paint has already got cracks in 4 places around the top.so my question is is it beacause fibre glass bumpers are crap or its a dodgy job.my mate has fibre glass bumpers on his skyline had them on for at least 2 years and i cant see a single crack in his paint similer to mine.

Sounds like a dodgy job. To paint fibreglass the paint should have a Flex-aid added to it to make it more pliable.