How do the price-compare apps get the products info and the price data?

Thare are many apps and sites can compare the prices of the sam开发者_StackOverflowe products at different places like different sites and different supermarkets,how do they get the products infomation and the price data?

Thank you!

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More often than not, through APIs provided to them by the merchants themselves.

See my answer here: How does a site that finds the best price among many eshops work ? Like pricegrabber

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Mostly via partnerships. However, screen scraping (web crawling) etc. are also viable ways.