Just got a random $10 voucher from ebay. Email says it is to make up for a recent 'bad experience', and that they are making up for it as I am 'one of our most valued customers'.
All I can think of was last week I asked a seller about an item that hadn't arrived for after a month, think it was a 'request' rather than a message, item showed up the next day so I closed the 'request'.
I guess you could try lodging a 'request' for an item then seeing what happens? Didn't cost anyone bad feedback or anything.
Unfortunately if people abuse this to take advantage of the goodwill gesture, eBay will probably stop offering it.