Rule #1 for buying a saw, used from a unknown source. (I.E., not from MM, or Landrum, or others proven sellers like that) is turning the engine over by hand.
Bought an old Mac off of fleabay. Good deal for it since it was complete... but it definitely needed a rebuild. Wouldn't turn over all the way. Found nut shells and composted nuts in the cylinder.
Tore it down and found a bad crank seal with a big crack in it. My guess is it quit starting easy and running at all due to the seal and they set it in the back of the garage or barn and forgot about it. Crank bearings were rough too. New ones made it a night and day difference.
Sometimes a saw that is all assembled and good looking can have a problem. Given the age of the saw I was buying, I expected it. I was just keeping my fingers crossed that it wouldn't be seized and it wasn't. Works for me.