You may want to look into the 2-of-3 escrow with timeout defined in BIP 112. https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki https://github.com/

You may want to look into the 2-of-3 escrow with timeout defined in BIP 112. https://github.com/bitcoin/bips/blob/master/bip-0112.mediawiki https://github.com/bitcoin/bips/blob/master/bip-0112.mediawi... You want 'the blockchain' to verify payment between parties; these parties will be in charge of verifying satisfactory delivery and releasing funds.