I would be hesitant with buying a boat that's been in the salt water; however, as a regular rider in the salt water, I will say that there are some boats out there that are just fine. I would highly suggest that you get the manifolds checked out before you buy it. Also, pull off some of the hoses check the color of the water that drains out, if it is discolored or brown that's a sure sign.
I usually ride behind a buddies MC prostar 209 in very salty water. We wash it with soap and water from tower to carpet and flush it out for a while every time. The engine had to be replaced last year after five or six years of being in the salt water and the guys at TSR were very surprised at how clean everything was, including inside the engine. So I'm told.
The main problem I hear about other boats in the area is that their perfect pass goes out really quickly. And the ones that don't take proper care of them have to be serviced often.
Moral of the story, If it's been taken care of you should be fine; but you have to do some digging to find out if the owner has taken care of it or not.