Who is deciding the Sold Price?

The Seller might think he's getting a great Deal until the Lender's Appraiser Shows Up.
Recently, in February, we Listed a one bedroom condo apartment for sale. The asking price was $399,900.00. A few days later, unexpectedly, we receive 4 offers. The best conditional (on Mortgage Financing) offer wins and everybody was happy. We were happy and the seller was happy. Next day, the buyer's lender sends its appraiser to evaluate the condo and decides that the buyer overpaid $10,000.00. The buyer's Salesperson contacts us with the news. We informed our Seller and the Seller accepts. We prepare an Amendment, both Seller and Buyer sign and the Deal firms up with a reduction of $10,000.00 off the original accepted offer.
Bottom line, the bank decided that the buyer does not get the mortgage unless the Seller agrees to reduce $10,000.00 off of the original accepted offer.