Originally Posted by Rover!
^ Furniture can be used by anyone, but an old rich dude's clothes are usually only worn by other old dudes.
This. Aside from a tiny and hyper-specialized auction market -- access to which will not be possible for you -- you will not have any luck flipping estate sale clothes for anything more than a few bucks a piece on eBay or B&S. And respectable auction houses would rather buy directly from the estate sale than from some middle man, whose items were of uncertain provenance.
Another sad fact is that vintage clothing isn't worth much to most people. If it has historical significance or is a famous movie prop or something, that's one thing. But if it's just some old man's old clothing, no matter how nice, nobody will care.