There are several ways an informant on a record can get confused. If a name on a document is totally incorrect, be open to the possibilty that the informant confused two people who shared a similar characteristic. If Grandpa sold his farm to a local auctioneer, your Dad, in remembering it, may accidentally provide the name of another auctioneer.
He had the occupation of the buyer right, just not his name.
Sometimes what's wrong may be partially right--just in a way you haven't thought of yet.