While browsing through stamps on Ebay a couple months ago, I stumbled across several listings that were suspect. Please note that these listings have since ended.

First example - Item #161694167835 was a multi-quantity listing of sheets of priority stamps supposedly printed by Stamps.com This seller has since pulled all listings.

2nd example - ezdxn is a Chinese seller who has sold similar stamps and received negative feedback alleging fake stamps. This seller has been suspended by Ebay