You do not need > 50% market share for the government to go after you for monopolistic practices. If Amazon made that case in court, they would be laughed out of the building.

> The simplest pro-Amazon case is that they do not have monopoly power, because they are not a monopoly.

It's also odd that their retail business doesn't make any money if they're supposed to have market power.

It really depends on how you define it, but Amazon, Walmart and Shopify are all excellent mainstream choices. This gives you plenty of numbers for comparison:

https://www.insiderintelligence.com/content/amazon-walmart-s...

Then obviously you're also got direct-to-consumer via your own website, and lots of niche channels like Etsy, Wayfair, and so forth.