The thing about buying used or "rebuilt" engines is you never really know. If you have the mind set that all used engines are pretty much rebuildable cores at best you will never be disappointed.

I have done some rebuilds that sat for a considerable time before they ran and they can get some rust in the cylinders. Alot of times it ends up superficial. If you would fire it up and not have disassembled it again you might never have known. You bag em up ya trap what moisture was there. Ya don't do anything and there is moisture in the air and some of the valves are open.

All used engines are "possibly rebuildable cores"