I was employed in management with a quality yacht builder
for several years. The question of liability for blisters
has been a difficult one for builders. Even today, the reasons for and causes of blisters
is not fully understood and there is still much disagreement among the "experts." I am no expert, but it appears that blistering MAY be caused by a number of very complex, sometimes interconnected, factors including resin quality, manufacturing processes, climate at time of lay-up, and water
Some builders will include a fabulous blister warranty as a marketing
tool. However, once you read the fine print, the warranty isn't all that great. For exmple you may have to return the boat to China
at you own expense to have any warranty work done on the blisters. Some builders do this because they know that blisters on a boat is still something of a "crap shoot." They put so many caveats into their warranties that they are almost impossible to enforce.
My best advice is to pay extra for an epoxy
barrier coat of specied mil thickness (if one is not included) before the bottom paint
goes on. Other than that I have seen many blister warranties as pretty much useless.