How to build an eBay / Amazon keyword research tool ?

such platforms doing ongoing heavy scraping and auto saving and monitoring the data .

others also comment please

ebay has one of the most powerful apis going

Terapeak has an exclusive deal with eBay and seems to be allowed to save data whereas most others can't. For starting a legit company, they handcuff you to signing an agreement not to save historical data. That's not to say you can't access it, though. For smaller scripts, like for dropshippers, they do give you an abundance of data to work with. Recent sales history, watchers, price history, etc. Amazon has a more limited API and you have to be a member of their associate's program to gain entry. I haven't played around with that one (yet). I've always hand scraped for data there. It'll probably be a let down when I do. eBay spoils the hell out of me.