In book publishing an author can purchase copies of their own books in order to increase purchases by others. This effect is actually common in many industries, even in mobile apps :)

So OpenBazaar's no worse than preexisting systems in this respect.

It's also borderline an unsolvable problem, because how do you identify "legitimate" customers in an anonymous de-centralized system, when it's even too complicated to achieve in a centralized system?

Assign a cost of creating a single anonymous identity: you've got to send xx amount of bitcoin to an unspendable address.

That is somewhat analogous to proof of stake, I guess?

And definitely in the record industry