1. As for "posted rates", I found the following definition.
"Definition of posted rate. posted rate. 1. The mortgage rates that the banks and other lenders publicly announce. Oftentimes posted rates are a full percentage point or more in excess of the rates banks are actually willing to offer, and the banks expect the borrower to negotiate the interest rate down."
2. "Credited to the buyer by the seller" refers to money/credit being added to the buyer's account by the seller, so it's the other way around.