Paypal is simply facilitating fiat money transfer.
I run a ebay store and my last invoice was $900AUD, for around $4k gross sales.
I only made around $1000 profit, so, my fees were equal to the same amount of my profit.
Literally half my money.
I do remember some brazilian person which has made an exchange with me some years ago from paypal to payza, where he offered 15 dollars for 10 dollars into his paypal, i got around 13 dollars as im a Euporean citizen, when i made the opost i got scared with the print, those person with the same ammount got a fee of 40% or something like that, i dont remember well. Soo if you do join paypal and amazon your potencial profit will be left into those two companies.
Well that is making them more rich and got more profit because of those high charging and unexpected fees. That is why I don't use paypal anymore and when upon searching something at ebay. It looks interesting but upon knowing their true identity that they are the same as paypal and other payment processor, I didn't tried to visit them anymore.