Lots of good advice ITT.
Here is my experience.
I paid 4200 for my 1999 challenger. The water test is what you need, the boat should function well..
Make sure to stop, turn it off, wait 10 minutes then restart. Run at all throttle positions, WOT and idle around etc...
My boat passed all these test well, and the engine bay was extra clean and looked well taken care of.
Sadly the boat sat outside uncovered (under a pine tree based on the amount of needles I have been pulling out of every nik and cranny) and weathered bad. Furthermore a bad attempt at cleaning the captains seats resulted in the seats looking like, well ASS.
So cosmetically on the outside my boat looked neglected, mechanically is was very sound.
I dropped it off 2 weeks ago at a Sea Doo boat Guru's house (his day job is working on these for a shop) and he is going through every inch of the boat, even is I have to spend another 2K I will be happy. The important thing to me is that is is in tip top shape, once he is done I will then try my best to keep up with the maintenance.
After I purchased this boat I immediately purchased a Sea Tow account then took it out 4 times at the end of this boating season, never a problem other than it developed a hart start idle problem. Hence the mechanic going over it. I instructed to rebuild the carbs, then do ANYTHING he could think of that the boat may need, if it is a common maintenance issue, DO IT!! This way I have a fun trouble free season starting this spring. That alone is worth the scratch in my book.
I am a motor head with cars, I am hoping that translates well into my first experience with boats.
FYI - Sea Doo jet boats are the only boats I would consider owning. Outboard and inboard motor boats are of no interest to me. I like this engineering.