If they have a monopoly control of the market, then the prices could be higher with sellers having little choice between paying and not selling at all.
Monopoly also means "exclusive or near exclusive access or control of something" for instance "she is monopolizing her time" and in that usage the original poster is using it correctly.
In fact, I think we should retire the term monopsony exactly because its actual usage is a subset of the usage of monopoly and nobody ever cares about the distinction.
I don't know if I would characterize them as having monopoly control of the market because nearly 100% of all of my purchases are made online and 0.0% of my purchases have been made using amazon.com (or walmart.com).
Generally speaking I prefer to buy a product directly, or from a specialized retailer.
Last week I purchased a stethoscope from an online stethoscope retailer. A benefit of doing this is that they offer laser engraving-- something that Amazon, with its warehouses of robots and robot-like employees, cannot easily do.
The specialty retailer also carries a wider array of color and finish combinations, because that's their product niche.
Using a specialist retailer has allowed me to flex on my fellow volunteer EMTs with a personalized Technicolor stethoscope, which is dumb but nice.
It depends on the exact market segment (Amazon does not have a monopoly on groceries, for instance), but yes, I think Amazon is effectively a monopoly. Or at least part of an oligopoly, which is no better.
I don't see how you can think this. Amazon is not the only payment processor, it's not the only inventory management company, not the only delivery company, not the only online store company.
There are any number of permutations of different service providers you could use to sell online. In fact, a very large number of people who sell online don't use Amazon at all. Or they will sell on Amazon as well as in other channels, or even direct.
Yes, I think you could argue Target. But Nordstrom? I don't think they have that sort of power.
Remember, an oligopoly (or even monopoly) doesn't necessarily mean there aren't other players, it means that the oligopoly is the only thing that can really influence the market. It's about who is writing "the rules", so to speak.
Amazon has a monopoly on creating a web page and selling and shipping stuff? There are literally thousands of merchants that setup their own sites or sell through Facebook, Instagram or Etsy