How do price comparison sites work?

Like Bizrate, Shopping, etc.

[fischermx]

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 :)

[Marcia]

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]

[macrost]

Marcia is definitely correct on the pay to play. If for example you take a look at some travel XML feeds they are very restrictive about the use and display of said content.

But of course, everything can be bought for a certain price.