[adingus]

After working with lots of different sized suppliers in the aerospace industry, the quality of your product really depends on your suppliers' culture. If they take it seriously, are willing to work with you and already ship good stuff you will have much better outcomes vs the opposite. Your best bet is to meet and talk with them a lot. Can you your their facility? To turn around a company that ships trash, you may have to acquire them... and not even that is a guarantee.

Beyond that it really depends on what you're manufacturing, and what you can spend. Look into PPAP (Product Part Approval Process) and take ideas from there. It is the process automotive manufacturers follow and will soon become an aerospace standard.