One other trap: the "zero hour" factory rebuilt engine.
Yes, the factories are the only organizations blessed by the FAA to 'zero hour' your engine. What is really means is that you get back an engine assembled of serviceable parts of unknown origin and unknown life.
Incoming engines are dissassembled and the serviceable parts are thrown in one large bin. Some crankcases / crankshafts may be on their third run or more.
"Zero hours" only means they don't know how many hours the newly assembled engine has. If you have a troublefree first run engine, might as well keep that even if it takes a few more weeks to complete.