> On Classfy right now you can add your forum username and the url to your profile. There is no way to authenticate the user but if many members from a forum join and list with classfy. We will arrange something with the owner of the forum to authenticate the users.

Pretend that I'm arn, running MacRumors. Why should I switch to your service?

My own "Marketplace" forum is working well. People who sell a lot on there have a reputation for not ripping others off. For those that are new, it's either caveat emptor or going through PayPal when something bad happens.

There's also Heatware already. It allows you to leave feedback for forum transactions. Your account is linked to all your forum accounts, so if you're new to one forum, but established in another, you have references. Here's my feedback page, for example:

http://www.heatware.com/eval.php?show=to&id=69703&nu...

They have around 70K registered users right now. If you want to displace them, it's going to be difficult (especially because people have momentum on Heatware already: they don't want to lose all their feedback to move to another system).