Looks good guys! Congratulations to founders on going live with the site! I'd love to try this out, but a facebook login wall is preventing me from doing so. I personally don't have an account, but I can see others not wanting to connect their facebook accounts with their businesses.
We're considering allowing users to have a Willet account (ie. new user name and pw). Aren't people sick of having so many logins these days? That was part of the incentive to use FB - keep things simple!
I think when you're talking about a payment integration system, having to create an account is not what will stop "sellers", as you call them, from signing up. It's probably different for end users though.