If the sails look and feel
as soft as an old flannel shirt, they are probably at or near the end of their useful life. While the needle test that Ross suggests is used by a number of used sail brokers, you'll need a seller's permission prior to poking a hole in his sails before you buy his boat. Sails, like tires on a car, are a "wear out" item and that eventually you'll need to replace them. When I bought my boat in 2003, I knew the sails were OEM and pretty much shot. I added up what a new set of sails would cost, divided by two, and subtracted that from the asking price of the boat....If the boat is in otherwise good condition, don't let the condition of the sails influence your decision to buy.