I don't know anything specific about a 1996-model-year Boston Whaler DAUNTLESS boats that would be particularly important to watch for when buying a used model. But that's not to say that someone else will know something important. But please tell us which model. Are you looking at a 1996 DAUNTLESS 20?
Boston Whaler boats are not like automobiles, in two senses. FIrst, they don't tend to change a great deal from year to year in their design or construction. And there are not detailed surveys of owners to provide data about repairs. Thus it is almost impossible to say that a certain model in a certain year will be likely to have a certain flaw, unless it is really a glaring deficiency.
The same general advice in buying a used Boston Whaler would apply as is given here:
http://continuouswave.com/whaler/reference/buying.htmlWhen buying a used boat with an outboard engine and a trailer--a typical package for used Boston Whaler boats--the boat is generally the most durable element of the package. Outboard engines are less durable, and a trailer can be quite a problem.
The boat's present condition has the most influence on value. The boat should have all the original components: the seats, the hatches, the railings, the navigation lighting, the various little components that will be hard to replace if missing, and so on. Owner add-on component may or may not add value. A poorly installed non-OEM canvas set can be useful, but might not be as valuable as OEM canvas. Electronic devices age rapidly. Too many add-on devices often means a lot of holes to be filled when you remove them.
Outboard engines are hard to assess unless you know their history, their maintenance, and their tendencies. Since you give no information about the outboard engine on the boat you are assessing, no advice can be offered, as it would be unnecessarily broad to offer suggestions about all possible outboard engines you might find on that boat's transom. Tell us what engine you may be buying and more advice can be given.
Trailers can be problems, particularly if they were seldom used. A trailer that has been sitting unused outdoors may need new tires, new brakes, new carpet on the bunks, new straps on the winch and hold downs--a lot of investment in small items that could add up to a lot of expense. A trailer that is used often to launch and load the boat will likely be in better condition that one than has been sitting for a decade unused.