If the plane has been run on Mogas most of it's life, run on Shell AeroSport 10-40w oil or Mobil 1 4T Racing full synthetic motor oil, and had the oil and filters changed at 40 to 50 hrs Hobbs regularly, had the air filters cleaned, had the carbs synched regularly, and the plugs changed within every 150 to 200 hrs, and the motor has 400 or less hours on it, it's probably in very, very good shape.
If it's been run on 100LL a lot, the gearbox will probably need inspection and parts replaced at 600 hours.
Keep the engine at as close to 2500 rpm once you start it up until your oil temp reachs 120F and then you do your 4000 rpm ignition check run up, to minimize wear on the gearbox.
For the most part, these are almost always low time engines and air frames, if you are buying a E-LSA version. With that in mind, get someone that knows RV air frames to inspect the build quality of the aluminum bits, check the engine service logs for the inspection annuals to note what was done when. The whole engine block and oiled areas are sealed from the external atmosphere, it's a closed system, and the bores of the engine are aluminum ceramic, so corrosion problems like in Lycs or Conti's is almost unheard of.
If correct oil, oil filters, air filters and such have been changed out annually or every 40 to 50 hours, I'd have high confidence that the engine is in very good shape. Check the prop too.
At Vy of 75 kts after takeoff, flaps completely up, you should see 5150 to 5200 rpms on climb out at full rich throttle, going straight out, if the pitch of the prop is optimized per Van's Specifications. You might see 5200 to 5250 with climb out at XC rate at 85- 90 kts, straight out, full rich throttle. You will burn about 6 + gals / hr at that throttle setting.
Rotax designs these to run on Premium 91 octane unleaded Mogas, not 100LL, which gums things up in the gear box and allows lead deposits everywhere. It's suggested you turn Mogas over regularly, NOT letting it get stale, by running the plane. If you must run 100LL on a longer trip, get some Decalin fuel additive to scavenge the lead out the exhaust system, instead of ending up inside the gear box and the crank case.