I'd be more alarmed if an older boat didn't have osmosis as you don't know what has been done to cover it up, I know of a guy who found lots of blisters under his boat so sanded them all flat and painted over them with antifoul to seal them, antifoul that well know porous paint that is designed to erode, It's still afloat 10 years on.....(same guy overheated so layed over the filler cap and undid it to top up, then waited for an ambulance while his face fell off)
Get a discount if you can but if you like the boat and price ignore the osmosis.