This morning while browsing eBay, I noticed a red banner on top of eBay's home page
It says "$5 off". When I click on details, it gave me a $5 off coupon (Expires 1/31 if I remember correctly). The catch is that it has to be used on that browser. It also happened that I did not sign in to eBay from that browser. (It was Windows FireFox in case you care).
Clearly, this is YMMV as I cannot repeat this on my other browsers, different PCs, different browser, even with incognito mode.
FWIW, I have used coupon to buy a $5 item and it worked. I paid $0. I also tried using coupon on another browser and it did not recognize the same coupon. I don't know if the coupon would work on items less than $5.