Checkout the insane amount of money Goodwill makes because of people getting rid of their "junk". There are 151 independent Goodwill organizations and all of them have a CEO, usually making 6 figures a year.
"Goodwill Industries was established in 1902 and is widely known across the country as the place where we all donate clothing and household goods to help others."
That's the first sentence from your link. Clearly people don't treat this org, literally called "good will", the same as they treat freakin eBay.
I don't think this is true, because people are often willing to spend a bit of extra time to do something good, like make a donation, but wouldn't be willing to take that same time to make $10.
https://paddockpost.com/2025/02/14/executive-compensation-at...
If people are giving stuff to Goodwill with no compensation, I'd say they definitely would give eBay stuff for a 30-40% cut.