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eBay has a program that helps sellers who want to contribute some or all of their auction proceeds to a charity of their choice.
The program is called Giving Works.
Perhaps you've come across listings with a distinctive blue & yellow ribbon icon next to them. That ribbon icon denotes a charity auction.
Many eBay buyers specifically look for charity auctions when they go to purchase an item.
These auctions typically bring in a higher closing price because buyers know some or all of the proceeds are going to charity.
An excellent example of an eBay seller using Giving Works is John (ColderICE ) Lawson. He is currently running a Giving Works auction where 100% of the proceeds will go to fight Breast Cancer. You can see him explain the auction here: