Repos and Impounds

I searched for information pertaining to this subject however I did not find anything. Does anyone have any experience with repo/impound auctions? It is my understanding that in order to attend most noteworthy (not your small local city) auctions you must be personally invited. Is this true? I have been to state fair auto auctions and whatnot, but the 'material' being auctioned off is generally not exactly high quality. Surely there must be opportunities to catch a deal on a nice bike or car, no?

Fred S