Will the paint fall off during sheet metal shaping? Post it.
If it's all sheet metal, don't worry about painting. Spray it anyway. If it's a machine suction piece, you must polish the paint surface of your concave piece before you can handle it, so the basic sheet metal and paint surface are not guaranteed. As for the paint cracking, it has something to do with the shop you are looking for. Good putty, drying and two-component primer will help reduce the chance of problems in the future.