Often the big blisters are only paint or lifted, thin gel.
A moisture meter the hands of less that experts , is the solution to determining hull moisture and blistering is a myth.
Again please dont take me wrong, the vast majority of biats out there are fine, even with a few blisters.
But like cancer, you just dont know by looking, sometimes extensive testing is required. And simple tests like moisture meters, tappings, etc may or not take you to the next step that really determines what is going on.
The problem with buying a boat us, you aren't going to get to the more accurate tests till you own it. So at least start off with the fewest symptoms and boat history.
From my experience, boats that live in warm water all year (like south Florida canals), that rarely get pulled out for paint and inspection and have lots of water in the bilge.....seem to have a higher incidence of hydrolysis than others. Not science, just my observation. Science does agree with the temperature affecting rate of chemical reaction.