Then there are books. All E-Books/Kindle.
A great place for little known authors to get better known, but a very cut throat environment.
Better in some ways, worse in others.
I wish the textbook industry was more competitive. When I went to college it was a minimum for $500 a semester in books that weren't always useful, but were "necessary" due to the racket between publishers, schools, and professors. $500 was if you got everything used at a good price.
I can only imagine how much a decent e-book would cost.
I wouldn't say sellers get screwed. It's just business as usual. Things get mis-shipped, things get lost, returned, broken on a pallet and not inspected. It happens, not that often, but it happens.
I used to be a warehouse manager for a relatively small network hardware place.
It's all in the logistics, and much of that comes from economy of scale.
UPS, Fedex, and USPS will bend over backward to make Amazon happy.
Not so for the small business.
(I had to get there at 7am and leave at 7pm most days. As Sales folks almost always make promises that cannot be kept.)
Who else has the capital for a couple completely automated million square foot shipping facility?
Then there is Amazon's "cloud".
You need a bunch of processing power fast you can rent it from them. WAY WAY WAY CHEAPER than buying the hardware.
Think cheeseburgers.
Would you rather sell a few $30 cheeseburgers, or a few hundred $2 cheeseburgers?
You make more immediately on the $30 burgers, but you make volume and repeat business on the $2 burgers.
It's a business of volume.