I read over the Marketing Terms of Use and didn't find anything about refunding fees. The c&p is from the TOU - there's more but this seemed the most applicable:
"Cost per Click Pricing.
If you participate in the Marketing Service on a cost-per-click basis, you agree to pay an ad rate selected by you in your account settings for each click on your Ad.
Cost per Sale Pricing.
If you participate in the Marketing Service on a cost-per-sale basis, you agree to pay an ad rate based on the final price of an item (excluding shipping charges and sales tax) for each Sale (as defined below). This Marketing Fee is subject to our then-current minimum and/or maximum rate and other requirements.
A "Sale" means an end user or device associated with an end user (an "End User") has (A) clicked on your Ad, which will redirect to the applicable listing, and (B) purchased an item featured in that listing within thirty calendar days of that click (the "Attribution Window"). In the case of multi-quantity listings, if multiple items are purchased from the same listing within the Attribution Window, each item purchased will count as a separate Sale and incur its own fee. eBay will be the final arbiter as to whether or not a sale of an item featured in a listing constitutes a Sale. You may end a campaign at any time, but you will still be responsible for Marketing Fees for Sales if the End User clicks on your Ad prior to you ending your campaign, even if the purchase occurs after the campaign ends."
Perhaps someone will ask Trinton where it states that the fees will be credited for a 'failed' sale - I couldn't find it (not saying much, of course 
).
