Forums: Discussions for entrepreneurs and small business.

Who collects/collates data for sites like ..Pricegrabber.com , gocompare.com , mysupermarket.com

These sites compare the price of an item found on multiple independent online shops !? How do these comparison sites obtain/collate all this data  ? Are there actual people that monitor each site / item / price and update prices ongoingly OR, do these sites enter in contract with each  shop and have pricing data delivered electronically .i.e database , web-service , excel sheet etc. ?