It appears that eBay is sending coupons to buyers who have left low DSR ratings for sellers or who have filed disputes with sellers.

Some sellers might say eBay is rewarding its worst buyers, those who are picky and complain. But you could reasonably argue that eBay is reaching out to buyers who have had problems to give them an incentive to purchase again from the auction site. (Assuming eBay could differentiate between buyers who have legitimate complaints versus those who are abusive or unreasonable, which is something I don't think that eBay has proven it can do.)
However, the bottom line is that eBay is giving buyers an incentive to give sellers bad ratings and to file complaints. ("Maybe I'll get another coupon if I complain again," they might be thinking.) That surely outweighs any positives that might be gained by such a program.
For that reason, this coupon program gets a thumbs down in my book.
Here's part of a letter I received from a reader about such a coupon he received.
Being both a seller and buyer on ebay I was very concerned with the following email since I did not complain to eBay or PayPal directly regarding any buying transactions. I did however leave POOR DSR's for a seller as the sale was less than favorable on all four counts. Now I receive a 10% off coupon worth up to $100.00 for my next purchase on eBay (see below)..... This is just one more reason that the new feedback system will fail terribly and buyers will be leaving less than favorable DSR's for sellers bringing the power sellers ratings below the thresholds for the incentives offered to them. I guess it is cheaper for ebay to give a coupon to a buyer for not being satisfied than paying a power seller 5-15% for being wonderful... One more reason to leave sellers less than favorable feedback...