Earlier quoted context omitted.
> I'm not sure that it can control prices Amazon very often competes directly with sellers on the Marketplace, and often undercuts them on price. There are products they sell below the purchase cost, sometimes below manufacturing cost. You can't compete with that unless you have piles of money to burn. They sell at a loss until they shake everyone loose from a product, then dominate all sales of that products on the…
So don’t sell on Amazon. There are tons of other options. Amazon is merely the largest, not the only.
At what point is it a defacto monopoly? A huge share of people shop exclusively on Amazon, particularly when compared to 10 years ago. There's no sign it'll stop growing any time soon.
Choosing not to, or being prohibited from selling on Amazon effectively blocks you out of a significant share of ecommerce sales. There's no way around that.