What he said is the truth. The Merc SeaDoo's were the B@atard step child to most of the seadoo shops out there. They didn't have the tools, or the want to work on them. Also... when they were cut in 2005... BRP had ZERO support. With that said... I don't know if that was a choice on BRP... When the relationship was cut... Mercury may have cut off parts support.
OK... with that out of the way... when maintained... they are VERY reliable. There is a tru cult following to Mercury Marine... and you almost have to forget it's a seadoo. (as far as power is concerned) If you need info, or parts... any Merc boat shop can get parts, and get you running again. But... unfortunately... some of the parts are very expensive.
But............
On the other side of that coin... A bigger seadoo isn't cheap to fix either. When you have a twin engine boat... and you have a failure... just assume that both sides need fixed. So... buying a 13 year old challenger 1800 will cost you $2600 for a pair of engines from SBT. (including shipping) Where a rebuilt 240EFI is about $3200. (so, it's not that far off) And God forbid you roast the MPEM in that 1800. First of all... you can't get one. If you do find one... it's $1600. But chances are... you will have to find a used one, or wire in 2 "Ski" MPEM's. (The MPEM is fragile) Where as... the Merc ECU is expensive... but I can go to a Merc dealer and order on right now. OR... get one off ebay for less than $500.
At one time... I was Anti-Merc. But now... I realize, you just have to get creative, and you can fix whatever is needed.
So.... what to look for:
1) Big holes are not good. (lol) Ok... I know... sounds like a joke... but seriously... it's a heavy boat... and rock damage is real. Get your head into the engine compartment, and look for patches. Get under it (since it's on a trailer) and look for large gouges. Ask the owner flat out... "Has there been any hull damage/repair?"
2) How does it run? These Merc EFI engines should start easy, and quick. After I did my rebuild (and got a loose fuel hose tightened down) My engine would start with a touch of the key. (hot or cold) I haven't gotten mine out from hibernation yet... but I'm betting it will start with less than 5 seconds of cranking. (once I charge the bat)
3) The smoke should be minimal. Heavy smoke at idle is a sign of a bad TPS or port side temp sender. The TPS is CRAZY expensive. ($500)
4) Make sure the pumps work. there are 3 pumps in that boat. There is the pond pump, the bilge pump, and the fresh water pump. None are overly expensive... but they seem to be bad when people buy the boat. Also... take the cap off the fresh water tank, and give it a sniff. It shouldn't smell nasty.
5) The new wear ring, and impeller are a good sign that the people maintained the boat. But... check the pump for corrosion. Also... get under it, and look at the intake grate. The stock one is weak, and known to break. If it's bent, or missing tines... that will need fixed.
6) general part movement. Check the steering, throttle, shiftier to make sure they are free. Also, check the seats, changing room lid, draws, and deck lid for function. Basically... open and close... or operate any thing that can move.
7) If you are really serious about it... and don't want any surprises... check the compression. It should be 125 psi or better for a healthy engine. If it has some time on it... it should still run down around 120. And... if they guys is willing... you can take it to a Merc dealer, and have them plug the scanner in, and they can tell you the history, and time.
8) THE MOST IMPORTANT THING: take it on a water ride, long enough to know if there is any issues. (Over heating, hard starting, loss of power, etc) You need to be out there at least 15~20 min. And... turn it off, and restart a few times.
With all that said... I dont expect it to be a new boat... and the price is good. So, weigh any issues you find to the price. But... under $10K... I would overlook some small stuff.
If you have any questions.... just yell.