I've seen few sales for CS:GO skins on this forum for cryptocurrency as of late; if you're looking to use a service to buy skins for Bitcoin,
Bitskins has you covered. I've never had to verify myself on Bitskins to buy a skin with Bitcoin, though you do need to verify yourself for withdrawals IIRC, but otherwise if you're only looking to buy skins that's not a bad site to go to. Bitskins usually also has the lowest prices I can find for skins as well.
I would suggest all prospective sellers to use escrow on this forum. Takes very little time to do so, and escrow ensures the chances of either side getting scammed are minimal.