Posted By:
warshawlawboth the seller and the interfering party can be held liable. The seller can be forced to complete the contract (specific performance) or if that is not possible because the item is already gone, he can be held liable for the value of the item not sold, less the purchase price not paid. The interfering party can be hit for compensatory and punitive damages.
Ebay rules aren't law, BTW; and asking someone to end early doesn't violate them anyway.