Ok, I see this going two ways now. 1. Revealing the price of the transaction could be optional, so it would only have to be revealed in cases where escrow services are used, although I imagine a large majority of transactions would involve escrow. 2. Prices of all transactions would be public. In this case, the entire market could be an extension of the bitcoin protocol, where the info about products, shipping address, the key signing stuff I mentioned above, become encrypted metadata associated with bitcoin transactions. You might say, doesn't revealing the price of each transaction violate the privacy I'm trying to create with such a market? Not really. The bitcoin network already operates this way. All transactions are public, but you don't know what they are for. You can find transactions involving hundreds of thousands of dollars, and they could be money laundering, funding terrorism, large drug buys, etc. The extended protocol simply includes that (encrypted) metadata in the transaction to create a market. Well, it's not that simple, there would have to be an elaborate key signing / management mechanism to allow third parties (escrow agents) to view transactions when it's necessary, and do all the buyer/seller stats stuff. Still, in case 2, it could be relatively easy to implement.