Not much. I clicked on "Report item", which is to the far right of the Shipping and Payments tab. That brings up three multiple-choice windows: Report Category (listing practices, in this case); Reason for Report (fraudulent listing activities); Detailed Reason (you suspect listing is fraudulent). That's it.
I don't know what eBay does with this info, but I suspect it generates an automatic message to the seller requesting a response within a certain period of time.
Possibly somebody else also flagged it, or his other listing.

Does anybody know for certain how eBay deals with flagged listings?