If there was a Piebald on Craigslist it was a scam. If you paid $700-800 for a low white Pied that would be pretty cheap.

Most likely they were selling a Het Pied, that mean the animal looks normal but carries a recessive gene. Again if you buy hets from Craigslist they are most likely not really a het, the only thing you are going on is their word that its a het.

This is a good place to look for Piebalds and get an idea what price range they are.
http://market.kingsnake.com/index.php?cat=32