Was it a crate engine that was bought and shelved? By dirty, do you make rust scale, gunky oil build up, debris, what is the definition of dirty?

If it was supposedly a new crate engine, you take an engine builder line BluePrint Engines and they run an orange dye in coolant passages and I think blue dye in the oil to check for leaks while doing their initial start up / dyno test, then drain it and crate it like that, they never flush them. The orange is misleading cause it makes the initial water orange / rusty looking and there would be a bluish haze in the oil passages & valleys.

One way to tell if it was ever ran would be to remove the head and see if you have wear on the cylinder wall or a carbon ring build up at the top of the cylinder.

Ebay buys make me leary, I've gotten lucky and burned on eBay.

Jim