Well it was never that hard to get extra suits when I was in, and they are AF issue. I would think one would get into a fair amount of trouble if they were trying to sell wearable suits while still active, but I don't know. After that though, they don't really want them back.
I have about a dozen or so flight suits. Patches and insignias are velcroed on, but there is no issue with selling those either.
It is kind of why you see all these military surplus stores. People sell their old uniforms. I got rid of all my BDU's and service dress at one of those joints.