friend and mentor had many 'discarded' boat engines behind the shop, and some rebuildable gems safely indoors. And he would always jump whenever he got wind
of an abandoned engine. They were an unbeatable source of spares he could recondition, and sometimes the engine was either a candidate or parts
source for a rebuild
So, I suspect it's not all that common for a non-insider to come across a rebuildable engine at a firesale price
.... but it apparently happens.
It was always my intention to buy one of his rebuildable 1 or 2 cyl Yanmars as an educational project
, but he closed shop and sold everything off before I got the chance.
. I'm still looking.