Specifically, do I have to pay some sort of fee if that happens?
There is no single answer.
It mainly depends on the product you auction, the type of auction and your account type.
Basically, your final fees come in the form of Insertion fees and Percentage fees
When you list and sell items on eBay, we charge selling fees. There are two main types of selling fees: an insertion fee when you create a listing, and a final value fee when your item sells.
The amount we charge depends on the item's price, the format and category you choose for your listing, any optional listing upgrades you add, and your seller conduct and performance.