Last month I made a purchase through a merchant covered by the Cashback guarantee, not huge, but enbough.
I was a bit surprised when the purchase didn't track, so I raised a query.
Now this has been rejected with the old "sale being attributed to another website or marketing channel", without, of course, suggesting who that might be. This is annoying because it is the one form of rejection I can do nothing about - because I cannot prove a negative.
However, it's a fairly stupid tactic as I have used and recommended them in the past, but will think twice in future.