E-Commerce Price History

What are the ways to go about for scraping data about price history of a particular product on an e-commerce site.

I see so many websites performing this practice on sites like amazon , newegg. For ex : keepa.com , camelcamelcamel.com

How do these sites go about performing this task as amazon itself does not provide a proper api for the sake.

The maximum period amazon provides at best is 90 days however a few of these websites provide price history data upto 2 years like www.pcpartpicker.com

Should we keep scraping every single product every day to create our own price history or is there some method out there ?