Just listened to a good story about art fraud on eBay on NPR. It's bent is fraud around the big names (Picasso, Miró , etc.), but it's interesting to listen to. You'll learn some language to be very concerned about if you see it online. Listen to it here (scroll down and click on Art Fraud).
Then there's this article in the Times about optimistic auction estimates in the big houses. Could it really be?