"If I list 24 units of a fixed price (BIN) item for $25 and 10 of them sell before the 30 days are up, eBay will credit me an additional $3 for each item that sells?"
Whatever you are using is illegal.
eBay will give you double the FVF discount you normally receive IF your listing offers free shipping and the items are sold between October 1 and December 31.
If an item sells for $25, your FVF would be (typically 12%) $3.00 which would be subject to a discount of 10%, 30% or 40% (depending on your DSRs).
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