In the fine print, it turns out that all donations must be made through "MissionFish." What's more, MissionFish takes a fee for its service. There is a small notice on each charity listing stating that a "small deduction may apply." Those words are in faint print and small type. There is no "may" about it, and the deduction certainly is not "small." In fact, MissionFish charges far more than eBay. That's right, you would be better off ignoring eBay's offer to waive part of its fees. Simply sell the item, pay the fees and donate the balance to charity. Far more will go to charity that way than if you take eBay up on its supposedly charitable offer.
Here is how MissionFish and eBay hide the fact that they are stealing from charities. Again, say you auction an item for $500 to benefit charity. The buyer sends the money to you. You then take the $500 and give it MissionFish, which tells you that you made a donation of $500. You never find out that about 15% of your money went to MissionFish.
Finally, eBay (which owns paypal) gets a fee when the money is sent to you by the buyer. So, you end up with less than $500 because paypal/Ebay takes a bite up front, but then you have to give MissionFish the full $500 so that MissionFish/paypal can take their next bite. And, if you forget to feed MissionFish the full $500, they will bill your credit card. Want to take your credit card off their account? No problem, just enter a new card and click that you authorize them to charge that. The website does not allow you to simply remove your credit card.
Do not be fooled! If you want sell something for charity, by all means do it, but do not tell eBay. Just sell the item and donate the proceeds yourself.