Before you buy a boat with years of paint build up...please read this:
Our boat had a lot of paint build up when we purchased it. We had it surveyed by a "reputable surveyor"??? The hull showed "acceptable" to low moisture readings.
The following spring of ownership I had the hull blasted...only to show what you see in the photo below.

Although the blisters were not deep, but about 5 the size of a nickel, it was still very upsetting to find out months after the purchase.
Knowing what I know now, I would have still made an offer on the boat, but a much lower offer, the equivalent of what a professional repair job would have cost or about $10,000 less.
My suggestion is if the boat you have chosen has a lot of paint build up it may be wise to ask the broker/owner if you can have a professional repair company take a few samples from the bottom and test for moisture and water damage, if they say no way, maybe they know something you don't???
BTW...my surveyor received a phone call from me after seeing what was present in the gel coat after the soda blaster did his work. He looked it over and offered his "professional opinion" on what was and what to do. I did not see the point in pursuing any legal action with the surveyor, I just wanted to get sailing, but I probably could have filed something with a good lawyer? My bad for not researching more before the purchase.