The seller of a defective item for online retailer eBay has the buyer to pay back the purchase price immediately. He can not hold back the money on the ground that the purchaser should withdraw its first negative feedback on ebay (Amtsgericht München, Az 262 C 34119/07).
This is true even if the assessment is incorrect. Although the buyer has a duty to withdraw the false statement. The seller should not hold back as long as the money.