Big deal...people donate really valuable stuff to Goodwill all the time without checking its value. Good for the people who spot valuable things, buy them cheap, and resell them high! Everybody is happy. The first guy got a charitable donation write off, Goodwill kept people employed and made a few bucks, and the last guy can make a lot of money.
I would say about 60% of my thrift store regulars are resellers. They keep us in business, we get to pay our employees, help the homeless and keep those resellers making money. We typically price things low so they will move. We also have an e-commerce team which I lead and we flip things like hotwheels and video games, action figures, toys, electronics for more money on the web. All of it goes to the mission.
I recently sold 24 redline hot wheels for 1200 bucks. Some things I really can not believe what people donate.