Hello Steembay...
The concept for your auction site using SBD as means of payment sounds great.
But if I were to buy something there right now, what guarantees can your sellers assure me of
Also , What happens if the seller refuses to honor the sales?
that's a good question. As everything can be traced on the blockchain, there is a good chance being able to legally proceed. I would not trade with someone without a reputation here, also you could use an escrow service. I also talked to anyx and bad behaving users can be reported to steemcleaners and will be blacklisted by cheetah.