[snakes1100]

Other than what you already posted, there is not a whole lot you can do.

You can use a forum to "recommend a sell/buyer" a feedback system basically. but other than that, not to much.

As for the waiting period, that isn't going to do much, as if i was the scammer and knew that, i'd just wait my time out and then post my scam.

You could do it two ways though and require a minimum posting req (10 posts) & the waiting period, but the user could simply wait out both limits, make the required 10 posts and off to posting scams again he goes.