Note that the Buyer has 3 days after the delivery date to decide on the acceptance of your item.
If the Buyer does not complete the transaction after the 3 days, the transaction will be deemed to be complete and final. The system will submit an automatic "Good" rating for you after you revisit your listing following the 3 days. To revisit the listing, just tap on the listing and the Automatic Buyer Rating will go through. Then you can submit a rating for the Buyer.
Note: the 3 days auto-completion is fixed on Gameflip's system. Our support team cannot reduce it.