mg, an OpenBazaar team member (I'll confirm his position) says this:
"I don't have a steem account to respond directly, but my suggestion re: "expensive" accounts would be to check how we're doing things with the ETH wallet. It also has a single address per user model which required us to build some smart contracts to handle escrow cases and an extra call to associate specific transactions with an order. This seems to be working well for ETH. If the Steem wallet were able to import an already made account for use, that might get you around the painful Steem account onboarding. I think the bigger concern that was raised was understanding how our escrow cases might work."
@swapsteem @travelersmemoire