I would trust banner ads more cause I think it's a lot tougher to scam people with them.  In fact, I can't think of a way other than the owners just randomly clicking to make it seem like people are coming to your site.  However, though, I really think with a professional marketplace there would be safeguards.

So anyhow, what do you trust?  I mean, assuming you simply cannot afford Bing Ads or AdWords?