Process verification

I am trying to tell if a company on Amazon is a legit seller. I am not a seller myself but is there any legal certification or something that needs to be submitted for the company to become a seller on Amazon? It’s a pretty large company and their site says they don’t sell on Amazon, but everything looks super legit on Amazon, shows posts, takes you to a “storefront” they only sell that brand.. I think their website needs to be updated, but how can I confirm on Amazon that it is verified and legit?