Funny story of how we came to exist. When XenForo was declared stable on March 8th 2011, we purchased an additional license (my third) just to say thank you the the dev's for creating such a great piece of community orientated software. So I was thinking, what do I do with this extra license. Understand now?
Anyway, I have been in the situation where I wanted/needed to sell off some of my vBulletin Licenses, and most of the popular sites which allow this, you either have to have a minimum post count or have to pay a fee before you can even list your item. NOT HERE. This is a 100% free service.