Buddy of mine is going through this right now. Bought a "just built, never run" motor from a well known builder. It sat for awhile after he got it, so he took it to a friend of ours to have it looked through. Compression is 3 points lower than claimed, pistons were so tight they would have seized if he started it, and the bearings were full of dirt. To top it off, the head on it was one another friend of ours had given the builder because it was junk.

As said before, I always treat complete motors as cores unless I know them well.