My employer sells stuff through Amazon that way. Amazon takes a cut on the transaction. There is a very small profit to be made by charging for shipping. It comes to far less income for the seller per unit time worked than even the minimum wage, but that doesn't matter to a charity that's using volunteer labour. Means the volunteers are really working for Amazon for free, though. I think it's pretty disgusting.

I'd bet that the workers processing the accounts are in some remote-working centre in the Third World and getting the same sort of wages you get for dismantling brake linings in scrap.