Seadoo's... over all... are probably more reliable than any of the other makes out there. (especially the 2-strokes)
I am a Yamaha convert.
With the exception of the 650 and 701 Yamaha engine... all of their other 2-strokes have about a 200-300 hr life, with proper maintenance. The bigger SeaDoo engines can go well past that.
I personally have a 96 Sportster boat and the factory engine was just rebuilt 2 years ago, and a 1990 Si that is still running on the factory engine.
Now... SeaDoo has a few things I don't like, but there is a reason for them.
1) the carbon drive shaft seal. They wear out, and will cavitate badly, but they won't let your boat sink. But they are relatively easy, and cheap to replace.
2) the plastic wear ring. If you are in dirty (twigs, and sticks) or sandy water, they will wear quickly, and your performance will drop. But, here again... they are cheap and easy to replace. On other makes, the pump body wears out, and it's expensive to replace.
3) you must use API-TC certified 2-stroke oils. They are expensive, but it's why the engine live for so long. There are other reasons for needing that kind of oil... but I won't get into it.
With that said... I would not buy a DI ski. When they work... they are great, and very fuel efficient. But, if you have a problem with it... most likely you will have to take it to a dealer to have them plug it in to find the problem. Also, the parts are very expensive. They have good reliability, but since you are looking at an 8 year old ski... things will start to wear out. I personally would look for a ski with carbs on it... and since SeaDoo has good reliability, don't be sacred off by a mid to late 90's ski if it's in good shape, and it has been maintained.
Good luck :cheers: