The mercury motors only have a "bad rap" with people who have no or little experience with them.
I agree, and disagree. So... here's my thoughts....
The bad:
1) They are expensive to work on, when there is a problem
2) On the 2001-1/2 and earlier engines... there is a plastic gear that drives the oil pump. It's known to fail.
3) They are expensive to work on.
The Good:
1) They run trouble free for +10 years !!!!!!!
2) Parts are EASY to get !!
3) The engine and drive is easy to work on.
4) Self draining cooling system.
5) They are salt approved, but you still need to do your cleaning/flushing after a day.
6) Very smooth running for a 2-stroke.
7) great customer support. I called about the oil gear during my rebuild, and I got a call back, and the guy on the phone was GREAT !!! even though, I was not the original owner, and it was WAY out of warranty.
OK... with that said... the reason they got a bad rap is because:
1) Seadoo used them for about 5 years... and when they discontinued the system... they also killed the support. (like, the next day) That pissed off a bunch of their customers. BUT... if you get one... just go to a Merc approved boat shop. (almost forget that it's a seadoo, because the dealers wont work on them)
2) As above, they run trouble free for 10 years. The issue now is all the seadoo/Merc boats are approaching that age. SO... they are starting to loose engines. If you buy one, and the engine has not been rebuilt... assume you will need to do it in the next year or two. Personally... If I bought a used boat, and it had a good running, original engine... I would take it apart, and do a basic rebuild before it has a melt-down. (it will be cheaper)
Just some random thoughts. If you find something... let us know.