When buying a used boat, you should look for any obvious signs of wear or stress on the boat's hull, such as corrosion or cracks, that could lead to a safety issue. You should also look at the boat's motor, if it has one, to ensure that it functions normally.
Anyone in the market for a used boat needs to know exactly who is going to use the boat and how they are going to use it before even looking at listings or actual boats. Having a strong understanding of the boat's intended purpose allows the buyer to build a reasonable set of expectations and narrow the search to specific models or types of boats, which helps the buyer avoid spending extra money. For example, if you plan on sailing with your large family every weekend, you need a boat that is in very good condition and is large enough to safely fit several people. In this case, you won't look at small boats, as they won't meet your needs.
Once you know what you want, you can make appointments to view boats in person. In-person inspections need to include inquiries about the boat's structural integrity and the overall function of any mechanical parts.