I Know that he already owns a boat but it's just like homes you want to trade up. It would not hurt if he invested in a moisture meter but don't tear up the whole deck because it had a low reading, a small leak can spread if you can find the source and fix it then wait awhile and test it again.
What I mean by a little while is let it truly a dry up then test it again to see if you got it. A pressure washer works real good if you are doing it in the summer when no rain. But if you are going cruising below 20 degrees South to 20 degrees North, don't worry about it, if it is a big leak and then decking is affected by of course tear up the deck and fix it.
I had a leak and the previous owner tried to fix it to no avail but a little new caulk around the anchor windless fixed it. And it was leaking in the saloon it was traveling all that way to find a place to drip and it drove me crazy trying to find it. I thought it was coming from my Bomar hatches but was just trying to find the path of least resistance aft and came down in the saloon.
The years thunder by, the dreams of youth grow dim where they lie caked in dust on the shelves of patience. Before we know it, the tomb is sealed. Sterling Hayden