In many areas of the United States, the summers are short, so don't just buy a boat before you really know what you're looking at. The first thing you should know is, there are three kinds of boats. An 'IO' which means Inboard Outboard. This is a boat that houses a regular car engine with the outdrive poking out the back of the transom then down to a propeller. The second one is an Outboard which can be a two-cycle engine (one that you need to add a special oil to the gasoline) and a four cycle outboard which needs no oil in the fuel and they attach directly to the transom of the boat. The third is an Inboard which has a car engine (or diesel) usually in the middle of the floor of the rear deck and a prop shaft goes from a transmission through the boat hull and then you have your propeller at the end of the prop shaft.  The main thing to look for is the engine and if there are parts available for it. Many parts for the outboard engines if more than 20 yrs old are no longer available. You can find them with a little hard work and possibly finding a dealer with old stock. You would want to ask a few questions on the engine like. What is the compression of each cylinder, when was the water pump changed, (it should be changed every year) If there is any water in the lower unit, (If the oil is milky colored, there is water in it and the gears can be damaged. A costly problem to repair) Ask if there are service records, or where they had their boat serviced; when; what was done etc. Regarding the boat itself, the floors of boats are generally not treated wood and can warp and rot. The seat cushions are mainly a piece of wood with a foam peice and covered with vinyl and stapled underneath to the wood. You would want to check to see if the wood under the seats is rotting or damaged at all along with the cushions themselves. Boat manufacturers usually only stock the material or cushions for five years and then the material is obsolete. If that is the case, if you call the manufacturer, sometimes, they sell the patterns and all the excess material to an outside dealer and they can help you get matching material or carpet for that year. The boat hull itself, you would look for gel cracks on the transom, the hull and any damage to the underside of the hull and chine areas. A boat does flex, so if there are gel stress cracks at the corner areas of the stern, this is sometimes alright depending if the structure of the boat is still sound.  Regarding the trailer, there are two styles. A bunk trailer that the boat sits on two or four long boards, and a roller trailer, which the boat sits upon rubber rollers. You would check the condition of the bunks for rotting of the wood, and on the rollers, they should be changed when there is a flat spot on them after the boat is off the trailer. Parts for roller trailers are much higher than a bunk trailer. I would check the wiring and lights for any broken wires, bulbs etc. A boat trailer should have bearing buddies or something similar and the bearings should be well packed before towing home. You would want to make sure the trailer is set up for the boat, because if the tires are too small, they will overheat and cause problems if towing something too heavy for the trailer. Make sure there is no cracking or problems with the tires. A bunk trailer usually has the boat sitting lower on the trailer than a roller trailer. There have been many changes over the years within the boating industry. If in doubt about a boat or what type of recalls there were, I would recommend calling the manufacturer and asking questions before spending money and getting something you can't use. An example is this. You could purchase a used boat that ran. You use the boat two times, and the engine fails. You bring your boat in for service and find out that the gears inside the lowerunit where the propeller turns are damaged and they are no longer available. There goes your summer and all the money you spent on your boat. Find out what you are buying and if parts are still available for it. That would be your best insurance.