re: What to know before purchasing a used boat?

Usually the seller will let you put a deposit on the boat that is refundable pending a mechanic check, sea trial, and inspection by a marine surveyor (if necessary depending on size/cost of boat).

Assuming everything checks out, then you pay the remaining balance. If not, the seller will refund the deposit.

I find that a lot can be learned about a boat from a quick look in the bilge. If the bilge area is clean and not full of standing water, oil/grease residue, and other trash, then the boat has generally been meticulously maintained. Sure, some dirt and grime is expected, but not an excessive amount. If there is water in the bilge, this is not a good sign. It has likely been there for a long time and has begun to soak into any exposed wood that may exist (especially true if its an older boat).