OpenBazaar can best be described as 'Diaspora meets Ebay'. It's a decentralized marketplace.
Bitcoin has largely made this possible, as it allows for multi-signature tranasctions, whereby m of n parties are needed to released escrowed funds. On OpenBazaar, 2 of 3 parties must to agree to make a transfer out of the escrow (multi-sig) address. Thus, when you buy something, you send your bitcoin to a multi-sig address. The seller then sends you the item. If you receive it and are happy, then you sign off on the escrow. Of course, the seller will too, so she signs off and receives the bitcoin. However, if there is a dispute, a predetermined third party notary arbitrates and eventually signs off to return the funds to the buyer, or on to the seller. Notaries will be rated by the community, and I believe they may charge for their service.
I think I might start selling paintings with OpenBazaar.