Not sure where you are but if you are in a cold climate, and the boat has been stored outside there may well not have been blisters on it last fall. When freezing occurs, they can appear. Basically, the water that is in the top layer of the hull under the
paint pools, and then expands. January and February are excellent times to inspect boats because of this.
Me - I would be worried. Regardless of what your surveyor says, before you buy the boat, go back and pop one of the blisters. If the fluid that comes out is colourless, and the blister drains quite quickly, it is only semi-serious. If the fluid that comes out is tinged with yellow or brown, you have a very serious problem, as the water has started to eat the styrene away. Also, if it continues to ooze, you know that there is a lot of water in there.
Personally - I wouldn't buy a boat that had more then one or two very minor blisters on it. My rationale is that anyone who let the blisters progress to a substantive point, probably didn't spend a lot of time maintaining the boat generally - hence there are liable to be other issues...but it's your call...