Here's my easy (non-scientific) way to tell an inverter generator from a non-inverter generator if you're unsure from the appearance:
Start it up without a load, and analyze what it sounds like. If it sounds like a lawn mower, it's a non-inverter generator. If it sounds like a well-oiled sewing machine, it's an inverter generator.
If it won't start up, it probably doesn't matter which style it is.
This may not entirely apply to larger generators. I've seen some large generators (diesel ones that are their own trailers) that were almost certainly not inverter generators but were very quiet and smooth. They were also more the size you'd need for a small campground, rather than for a single RV.