Browser extensions for Coupons and Deals


I’m doing some research on the various browser extensions or add-ons that can get you coupons. Basically I would like to know how they are able to get the data. I know these tools so far.
wikibuy, honey, camel camel camel and earny, but wondering what APIs they use to get such data or are they simply crawling the web? Is it legal to crawl the web and find the best deals and make money on those deals without content owner consent? I appreciate if someone provide some useful info or pointers related to my question?

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