This thread has taken a wide right turn.
You can use a moisture meter, you can tap with a rubber mallet to hear for dead spots.
But based on the OPs post, I suggest
learning a lot more before
buying an old
boat. There are many helpful threads on this forum on how to self
survey, things to look for etc...
When you have a
boat in mind bring us some specifics.
As far as old hulls go, in general a good
hull is a good
hull. New or old. Anything CAN be fixed, just requires time and
money.
Nobody can answer your question on if you should avoid a boat or not. Most people would tell me to stay away from my boat and I love it and it's been good to me. You have to do an honest assessment on what you can handle, and what you're willing to take on. Will you spent 20 hours in your
bilge reviving your old
motor, or will you have to pay someone to
service it or swap it. Can you stand crazed decks or do you want the Yacht look.
What's your sailing experience? Do you know what you really want in a boat? If not go get an inexpensive boat and sail it for a year, a lot and figure out what you wish you had. Keep it around while you start your
project and move from there.