I don't mean to cast aspersions on your friend's airplane for sale, but he'd assuredly get more interest in it if it had a current annual.
I'll add a dissenting note. Fresh annual on an advertisement almost invariably means the annual was pencil whipped or nearly so. Owners don't fix stuff on airplanes they are about to sell. I've represented some new owners who were excited to buy a "fresh annual" airplane because they could fly it for a year, and didn't do prebuy exams. They spent a LOT of money making those airplanes airworthy. I saw two "fresh overhaul" engines that had logbooks that said they'd been run 2 hours on a dyno. However, they didn't even have ignition harnesses.
Do a careful prebuy, no matter what. If you buy it, have the tech who did the prebuy do the extra work to make it an annual. Peace of mind.