This is a common misconception. As has been stated before on similar threads, Amazon comingles inventory. So if you as a third party seller have a bunch of fake widgets for sale on Amazon and anyone else (including Amazon themselves) sell the same widget (same by name) then Amazon has no control over whose inventory a buyer receivers, regardless of the Sold By label on Amazon.com

https://www.wsj.com/articles/on-amazon-pooled-merchandise-op...

Relevant paragraphs if you can't get past the paywall:

"As more third-party sellers have signed up to offer products through Amazon and use its order-fulfillment services, the Seattle-based giant has allowed many to pool their inventory with supposedly identical items supplied by other sellers—in essence commingling products from third-party merchants with those supplied directly to Amazon by the brands themselves.

In other words, a product ordered from a third-party seller may not have originated from that particular seller. If the bar code matches, any one that is on the shelf will do."