Welcome aboard
@Daveaddy. These boats are very reliable however, they are not meant to be kept in salt water for extended periods of time. A few days to a week at most at a time. The engines also require a flush with a solution of some sort of salt eliminator like Salt Away and fresh water after each use.
In looking over the boat, general condition of the boat will tell you if the previous owner took proper care of it. Look for dings and scratches in the fiberglass hull. Check the seats carefully for wear, cuts and holes. Also open the bimini and make sure there are no holes, rips or a bent or damaged frame. I would also put the throttle levers in forward, go to the back of the boat, on the ground, reach into the jet nozzles and feel the impeller blades to see if there are any nicks or damage. There are 3 blades on each impeller for each engine. Check the anodes for wear while you are there. Look closely in the engine compartment. Is it clean? Are there any signs of water such as rust on the hose clamps or a water line on the inside walls of the compartment which may indicate the boat may have taken on water at some point? Check the oil on each engine. Is it clean, proper level and not milkey?
Carefully look over the trailer. I'm assuming it's a galvanized trailer for salt water use? Check for rust, tire condition and condition of the carpeted bunk boards. I would walk on them to make sure they're not rotted under the carpet. Also check the winch and winch strap. It would be easier to check thè trailer when the boat is in the water.
Is this dealer an authorized Yamaha dealer or is there one near you where you can get parts and service if you need it? It's a little surprising the dealer won't give any warranty. Are they not confident it is a good boat? If these are not common boats in your area they may be willing to give you a good deal to get it off their lot. How long have they had it? Take a lot of pictures and post any here that are a concern to you. You can also post questions while looking at the boat. Hopefully someone will be online to respond.
A test ride will give you more information. After running at slow speed for awhile run it up, quickly to full throttle and make sure it makes the transition to full speed without stumbling. Check all running components like the "no wake" system, lights, horn, blower (blower should be run for several minutes before starting the engines). Run the radio before or after your test ride so it doesn't mask any boat sounds or issues.
These boats are much easier to maintain than most. This forum is a great support system for the few issues that may arise. Keep us in the loop during your inspection of the boat. One more thing...If this dealer is not a Yamaha dealer it is very likely he is not familiar with operating this boat. Make sure the clean out plugs (under the rear hatch on the swim deck) come out easily and are properly installed and latched. This should be done prior to launching the boat for the test ride. If they are difficult or impossible to remove that would be a concern but not necessarily a deal killer.