And the answer is simple: treat them as early adopters. Learn from their needs, and find out how they attempt to game or break the system. (They certainly will.)
No, I'm not trying to be flippant. For ANY new, more privacy-minded tehnology, you have to expect that the dubious and/or illicit users will flock to it first. They are the ones who will actively seek out the communication and exchange mediums that are hard to monitor. Their presence will then act as a catalyst for media to write about the technology, effectively taking it from the fringes to mainstream.
PGP. Tor. Bitcoin. Hell, even the attacks on encrypt-by-default storage technology in mobile phones. The fearmongering of the law 3-letter agencies and the media's need to find new monsters under the bed all act as drivers for more widespread knowledge, and eventually through acceptance to adoption.
The pendulum swings, and right now it's starting the backswing towards more privacy-minded approaches.
Yes, but I would argue that doing so in this case means undermining the entire purpose of an anonymous, decentralized marketplace.
The first question most people are going to want an answer to when presented with something like OpenBazaar is "what are you going to do about the pedophiles, gun-runners, drug dealers, etc?"
If the free market's response to this is "nothing, so long as the customer gets what they paid for, everything is cool," then for most people accepting this equivalence will be a non-starter.
I think the only ways to avoid this problem are 1) hoping for a widespread shift in the way most people view the value of the force of law on commerce, 2) breaking the system enough so mainstream users are convinced of its legal integrity, or 3) pretending it's not an issue and redefining the terms by which it's sold to the public. And i'm not entirely certain the latter can scale.
I won't say it's impossible though.