https://www.cnbc.com/2021/05/07/amazon-mails-postcards-to-sellers-to-prove-their-addresses-are-real.html
It seems quite a basic check to me, that I am surprised they have not been doing it all along.
I seem to remember getting post from them when I set up.
https://abcnews.go.com/Business/wireStory/amazon-blocked-10-billion-listings-counterfeit-crackdown-77595052
I guess all this cleanup activity is due to:
https://www.engadget.com/amazon-third-party-product-safety-court-ruling-151546590.html