Rule 1: Don't buy anything without a Rotax 912 or 912S in it.
First, it will save you bags on fuel. Second, you will always be able to resell it.
Two-strokes are unsellable - no-one wants them. They are perceived as less reliable, the days where microlight instructors earned a few bob decoking them etc are long gone, they use more fuel, they are noisier, people can't be bothered mixing fuel (or even topping up injection reservoir), need I go on.
Here at Strathaven, we have decided to ban non-Rotax engined aircraft from being hangared here (with the odd exception for historic or very unusual stuff) to save people from themselves!
Yes, lots of people will come on to tell you how wonderful their two-strokes are, but.....