When purchasing a used boat there are a number of things you will want to look for to assess the quality of the vessel.
Starting on the outside, you will want to check for corrosion on the out drive or lower unit. Make sure the cables are in good shape and also that the prop looks to be in good condition. Make a visual check of the fiberglass exterior. Make sure the rub rail is intact and not excessively damaged. Also look at the hardware and the gel coat to make sure they are good shape.
The trailer is just as important as the boat. You will want to check the wheels and axles. If there are brakes, you will want to check those as well. Make sure the lug nuts are nice and tight and that the tires have some wear left on the tread.
Inside, take a look at the upholstery. It will likely not be perfect, but check the stitching to make sure it is solid and for any excessive wear or tears that need to be repaired. Walk around the floor, checking for any overly soft spots. If it has some give to it, that might be a sign of concealed damage.
Important safety systems to check include the bilge pump and the battery. The blower on an inboard type engine is important as well, to keep the engine cool. It’s a good idea to check the oil and other engine fluids. If the oil isn’t clean, that is a good indication that proper maintenance may not have been performed on the boat regularly.
Check the engine for excessive corrosion. Keep in mind that it is a used boat, so it won’t be factory perfect, but a heavily corroded engine is definitely a red flag.
A water test is imperative. Get it out on the water and test all of the systems to make sure they are working properly and to also determine if you like the feel of the boat.