There is a colossal fulfilment center (amazon warehouse) within 20 miles of my house. They actually pay at least local average wage or even somewhat better.
A little surprised, but we have a saying here about not "shitting on your own doordtep"!
The rumours in the UK were of almost Dickensian work conditions: low wages, very strict rules etc. Not actually sure if that still applies.
On Joeactor's comment on raising prices . . . They did, of course, scrap totally free postage yonks ago. Don't sell enough to notice if selling fees have increased.
Seller's set their own base prices but a lot of stuff comes from China. Really cheap and often nasty. It was iften said the Chinese plot was to destroy Western industry then hike their prices. There has been some social and industrial action in China against the poor working conditions and wages and poor social services. Improving these will cost a lot of money and China's GDP has suffered a bit.
The price hike msy not be far away but maybe not due to Amazon's top of the tree position. Though, since seller fees are a percentage, such a hike will help Amazon grow.