Question on Engine for sale.

[zaueugen]

I have a spare engine lying around, has about 140k miles, wanna sell it for 400$. The problem is I pulled it out from a car and never actually started the engine before pulling it out, because the car had no transmission or battery.. The guy I bought it for told me the engine ran fine. Is there and way of knowing if the engine works properly or not or not without having it installed? I don't want rip anyone off if I sell it.