I'm a complete novice to the world of comparisions sites in terms of how they work and the process merchants go through for its products to end up on a comparison site and I would be most grateful if you could help me understand this better.

Each merchant signs up to a comparison site i.e. pricegrabber, pricerunner wishing to display it products.
Each merchant creates a file called datafeeds (csv tab delimited or xml format) which consist of all its product information.

Datafeed questions:
1) What are merchants using to create or build such files, is it using excel, notepad or can it be formed based using php/asp scripts where they just enter the details one after the other that the comparision site has developed for them.
2) If is not formed based, how do merchants know what format to enter the details in. Are these instructions given by comparison site.
3) Say 100 merchants submit a 100 datafeed, will the comparison site search all 100 files looking for the products requested?

Once the comparison has the datafeeds and a search is performed, obviously it will output the relevant products linking to the merchant site. Once the links is clicked then the product hopefully bought the comparison site will get an agreed percentage.

this is the way i think it works so please rectify me if I am wrong

Thanks for you help