Purchasing an engine "as removed" has risks, as you can only go by what the seller tells you about it. You may never get the true story on how it was operated and maintained.. The biggest question on this type of engine is WHY was it removed?
When you buy a used airplane, it usually comes with a used engine. That it's currently installed does not mean it didn't clip a taxiway light, get run low on oil, or suffer other mistreatment some time during its life. Again, you're going by what the seller tells you and any info that's gleaned from the logs (hint: Not all information makes it into logbooks).
As a guy who scraps airplanes on a regular basis, I can tell you that good mid-time engines find themselves in need of a new home for a variety of reasons. I don't understand why you're harshing on the idea of buying a used engine.
