How does a site that finds the best price among many eshops work ? Like pricegrabber

I saw a website http://www.pricegrabber.com/nokia/products.html/form_keyword=nokia/st=query/sv=findit_top/ that finds the cheaper/best price of a product among many eshops. Their system searches through their database (I guess they are using XML) and displays all shops that have the product sorted by price.

I believe that their search function looks over a united XML of all the shops. But my question is, isn't supposed all those eshops that incl开发者_开发技巧ude in the site, should have the same XML structure? How do they manage to do it ?

If my idea is wrong please tell me how does this can work.

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Often, the sites being compared willingly offer up their prices to the comparison site (via an API, webservice etc.) rather than getting scraped against their will.

From their perspective, anything that draws some extra visibility is a good thing. They normally pay the comparison site a small affiliate fee for every sale/customer that is referred to them as well.

GoCompare, CompareTheMarket et. al. don't exist to be helpful out of their own good nature - they are getting a cut of profits and the sites they feature are complicit in providing them with the data.

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The nice way is to get XML data from each shop and then group everything to display to the user. Since there is no standard format for this, your site must have a specific backend for each shop.

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Each web sites submits a csv file with all their product information in the same format to pricegrabber. Pricegrabber then imports that data.

You can do the same by signing up a to an affiliate network and like CJ. Once you have an account you can download product data feeds from merchants that provide them. You will need to match up any item with the same SKU or by brand and MPN. Matching the same item to different merchants is the hard part.