My main concern is how do they get the data? Do they have to write custome robots/spiders/scrappers to get all the product information from the main merchants? Or is there some kind of xml feed format/standard available which they use to share the information? Anything you know about this topic is welcome :)
It's pay to play, so my guess is that the products must be specifically chosen by the retailers to be submitted (rather than scraped) to them for them to promote.
I do know that in some cases the shopping sites (like NexTag) buy from ad serving networks; there is at times behavioral tracking & marketing, and when products are promoted, it's for specific retailers who the consumer has clicked over to from the shopping site. I know that from my own experience when logging into my ISP web based email.
[edited by: Marcia at 6:36 am (utc) on Dec. 21, 2008]