1) I don't understand why there is a need to encrypt data and send it over the Bitcoin blockchain, it will be there forever and if someone can decrypt it then everyone will know what you bought, and since we are talking about peer-to-peer networks it is better to destroy everything after the trade is finished.

2) You did not mention how to deal with scammers, will the service provide a guarantee? And if so, what will the guarantee be? Or will it rely on trust points?

3) Wouldn't it be easy to fork OpenBazaar and create a highly private shopping service that is available to everyone?