While I'm sure that many good engines are sold on the internet, I've even sold some. The phone call that make us cringe is the one that starts with " I just bought an engine off the internet".
If I had a buck for every A&M clunker that was sold as a Walker or Plane Plus Eaglet I could buy a 35% Cap with engine.
Pictures help, but hands on is best. Like they say " buyer beware"