I'm just curious what made you willing to trust this site?  Seems like you could take that 3.5 BTC and buy 2 more of those coins from here to sell on that marketplace.  I know with a 250% premium on Casascius coins I would sell my entire collection.  I feel like this might fall into the too good to be true category.  The whole idea of sending them your coins in exchange for an NFT smells a little.  I'm happy for you though.  Were you ever worried you wouldn't get paid or that they would take your coin?  I don't think I could have taken such a risk.  Glad it paid off for you.  It must have felt great seeing those coins hit your wallet.  I hope others have a similar experience.