Wood boring insects generate "frass", or poop. The frass looks like the black toasted poppy you get on a NY Bagel. Sometimes the color can change, based on the type of
wood the critters are eating.
Wood boring insects needs two things- wood (duh!) and fresh
water. Without either they cannot survive. You can exterminate all you want, but that will not solve the problem. If you kill the living bugs, there are still eggs. The eggs will
hatch, and use the
water leak to digest the wood and much away at the sailboat buffet.
The wild cards are--- did they get into the
core between the
fiberglass? Did they weaken any bulkheads?
The boat has to be a hell of a deal, you have to be willing to deal with the pain of exorcising the bugs, and fixing any damage.
Unless you are REAL good, I would walk away.
PS- you have better shot of an ice cream sunday in hell than getting a fair bug inspetion on one of the island.