At that point just don't buy any coin that you can't trace the origin, even partially.
You mean provenance? That is a good idea but how do you do that with these coins? Especially redeemed ones? I know some people have bought directly from Mike and thus know where the coin came from but otherwise how would that be done? I was fortunate enough to buy a silver gilt 2013 1BTc directly from Mike right before he closed shop in 2013.