Buy the boat. If it doesnt have blisters after 18 yrs, it probably
wont get them. Blisters are only cosmetic nearly all the time anyway.
Blister repair, even the gelcoat peeling type is a great scam for boat
yards and rarely solves anything. If you are worried, please show me
one documented case of hull failure from simple osmotic blistering. It
simply doesnt happen.