How do you find out if a product is selling well?

You know how there's websites that post tv ratings to let you know if a show is doing well? I was wondering if there was any kind of website like that but instead of with tv shows, they tell you if products (such as dolls/toys/games etc) are selling good? Maybe like a financial website or something. If you... show more You know how there's websites that post tv ratings to let you know if a show is doing well? I was wondering if there was any kind of website like that but instead of with tv shows, they tell you if products (such as dolls/toys/games etc) are selling good? Maybe like a financial website or something.

If you know of any website like this could you please give me a link? Thank you!
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