Authorized Digital Sellers
/ads.txt
(spec)
Defined by the IAB Tech Lab, ads.txt allows sites to specify which ad system accounts are authorized to sell their ad inventory.
Ad Sellers
/sellers.json
(spec)
sellers.json is another standard by the IAB Tech Lab that is related to ads.txt and app-ads.txt.
It allows ad systems to provide details about the ad seller accounts listed in ads.txt and app-ads.txt resources.