Whats it worth 318 fresh bottom end on Craigslist

How much are they asking?
Why is seller selling prsumably at a loss?
engine that you know nothing about..
Is the seller offering a warrentee?
Was the work done by a reputable shop?
does the seller have reciepts?
What parts were used?
I'd go to an engine builder and see what they charge for what you are looking for.