That's what happens when Amazon has a monopoly. Many customers will only look on Amazon and won't buy anywhere else.

Back in 2003, people were saying the same thing about walmart. This article talks about how the demand for 'lower prices' almost drove a pickle company out of business:

https://www.fastcompany.com/47593/wal-mart-you-dont-know

Yes, Amazon is doing a lot of the same things that Walmart did back in the day.

But if they don't sell what you want you'll buy it somewhere else... Ebay is still a thing.

Sure, but simply raising prices doesn't have that same effect.

While it is a risk, it can be a calculated one. Most household goods require the "platform" of a supermarket or other merchant to actually reach customers. Is this so different? As a consumer, there are lots of benefits to being able to find and discover goods in one place, and as a seller, access to those potential customers can make or break your business, but might not be something you can actually establish effectively on your own without those distribution channels. The same is true of infrastructure - one always has to weigh the risks involved against the costs of trying to do things yourself.

This is certainly true on the low-end, but rarely true on the high-end. Especially when we're talking about kitchen products. The most expensive, sought after fridges, stoves, espresso machines, etc aren't found in retailers.

The problem is that Amazon's goal is to replace retail stores with their website and to build a monopoly on consumer commerce.

Competition law exists precisely to stop monopolies from saying "it's our business so we can make the rules".

Name a livelihood not dependent on someone else.

That was not the argument the OP made. The argument wasn't that other people aren't necessary for income. Their argument was that relying on one, and only one 3rd party platform for selling things online was a bad idea.

If your career and income are entirely reliant on one company, regardless of type (tech platform or retail or college or whatever), you're beholden to their whims and whether or not they stay open. It's a good idea to diversify your income if possible (via savings and investment if possible).

Further, this is even more of an issue if your income is selling and buying via online platform. They may not shut down, but they very-well may change the TOS to exclude your type of selling. . . . Which is what this is.

Ah, I'll buy that. Don't put all your eggs in one basket. Fair point.