You should have had a contract with terms explained to you before you listed the property for sale. $8,500 for a house that sold for $32,000 is extreme --- if that is the commission portion of the sale. If an agent came to you with these terms you should have kicked him/her out the door and called someone else.
Please realize, however, that there are also title fees, taxes, county fees, and other factors that can lower the net proceeds to the seller besides the real estate commission. Your HUD Settlement Statement will account for every penny of the transaction. Remember, property taxes are paid up through the day of settlement, and they can be a big deduction.