Since the coins have been confiscated they are by definition "dirty", otherwise I guess they wouldn't have had the legal basis for seizing these coins (unless we're talking bankruptcy cases)
Either way you'll be able to prove that you've bought the coins at the auction, making them "clean".
Kinda silly, isn't it.
governments are the best damn money launderers on earth---steal a criminal's coins, polish them up, and sell them at a premium. rinse/repeat. the police have turned asset forfeiture into an industry at this point. why not bring it to crypto?
if you get coins in a government auction, those coins have been issued a clean bill of health---literally endorsed by the government. compare that with coins freshly withdrawn from a darknet market, which could be flagged by any exchange you send them to.
which coins seem dirty and which ones seem clean?