Ive been designing resins for 25 years. With all the customer complaints that have occured over the time the one single consistancy has been poor preparation.
If you first sand blast to break up the surface so as the coating has a greater surface area to grab your on your way to less chiping.
Then any quality pwder coater will totally wash the part to remove grease etc,
Then ask what product they use. Akzo Nobel and Dulux are first rate
Preparation !