Well, Blueh's basically got it, although I still think event hats could be traded, as a lot of events are luck based and not really earned and that few of them exist in some event hat cases. Or maybe someone doesn't like their prize. Guild hats, RPS hats, and any other earnable hats shouldn't be tradable. Currently sold hats show a price, while hats that are unavailable wouldn't show a price to signify that it isn't/never was sold. I forgot everything else I was going to say. ._.