The ability to win the buy box is exceptionally predictable.

It is based on a combination of factors. The price point, fulfillment method, shipping cost, and feedback provided by customers about each individual seller.

If I am the brand owner, using Fulfillment by Amazon, have the lowest price, and good seller feedback, I will win.

If you come on the listing a lower price, no shipping cost, and equivalent feedback, but you are shipping the item yourself and have a slightly lower feedback rating, you will not win the buy box.

The system is not rigged against the customer. Amazon is attempting to improve the customer experience, with price just being part of it