i don't know if this has been covered before. is there a way/technique in identifying a turbo being sold to you especially used ones? lets say if a seller from ebay or a shop is selling used turbos whether oem or used ones, how would you if what you're getting is the real deal? like if he claims it's t3, t28,t3/t4 and so on, is it possible to identify it when there's no markings on it?

thanks.