First thing I would do is have him put a 20 shell into the gun. More than one 16 has been listed and sold as a 20 on Gunbroker. Most by mistake, but a few intentional. A 20 is far easier to sell than a 16 to most buyers. After all everyone knows they don't sell 16 shells anymore. And returning a gun listed as 20 which is a 16 is a real hassle. Been there and done that.
Funny how many photos are cropped to not show stuff I'd like to see. Like the choke markings on the barrels. There is one gun on Gunbroker which shows multiple closeups of the sides of the stock and barrels but zero full pictures, no views of the receiver and no view of anything where you could judge wood to metal fit. Worse you can not figure out what model the gun is based off the listing and that makes it impossible to figure out if the gun is worth anything or just scrap. Funny how bad photos tell you as much as good photos sometimes.