When you click on it you get an Ebay page with search results for that product.
don't underestimate their ability to know ROI at the deepest level...
I heard the guy in charge of their PPC at Ad:Tech San Francisco this year, and from what I recall, he said that they worked with so many words that they have deal with them in large groups (buckets). So they take a bucket of words and see how it sticks. The impression I got was that the depth of detail was closer to a macro than micro focus.
they know not only what the initial value of a new buyer or seller, but also the long-term value of each type of customer that comes in.
PPC people often focus too much on each sale, and not the value of a lifetime customer. Sometimes I get asked by competition how I can afford some of my bids - and the answer lies quite easily in front of them.
I am thinking of a friend who went to the site of a 'famous outdoor supplies store', found a huge sale going on, and happily bought a bunch of stuff. Most likely she was being tracked, and the site probably recorded one conversion.
What did my friend do next? Well, she emailed about 100 friends and sent them the link to the sale. A lot of the friends also went online and bought clothes, shoes, tents, and all sorts of other stuff.
Almost certainly, a few of those hundred friends emailed the link to other friends, although I can't vouch for this.
Bottom line: hundreds if not thousands of dollars of business, but only one conversion recorded for the person who started it all.