How to sell a used engine?

I wouldn't pay a whole lot for it without being able to listen to it run, drive it, etc. Without that, its just a core until proven otherwise. In fact, I'd say that unless it runs perfect the buyer should consider it a core. It may be that it doesn't idle because of a vacuum leak or timing, or because its down a cylinder. Until its proven (ie, fixed), you don't really know.

A compression check might make me feel a little better, but the 318 in my Duster has GREAT compression and still smokes like crazy because of the valve seals and guides. But I only paid $250 for it, so its not a huge deal. On the other hand, had I seen it smoking before I bought it, I probably wouldn't have bought it.