I can't find a feature request board for this and it crosses over with classifieds which has got a feature request board but here goes...
When one clicks on buy now you have to be a registered member of that forum to purchase and administer ads. Could this be integrated with the membership registration of the site if you were only a guest? Then, not only would it create an account for the guest to use, you could add that new member to an ad buyer group, where other privileges could be assigned? You could even integrate it with social media sign up so that they could sign on with Facebook, Twitter et al?
What do you think? Good idea or just pants?