It sounds like you made a purchase from someone in the US. There is a new program (Global Shipping Program) that some sellers are using in which international buyers are charged up front (instead of at the post office) any import fees. There are incentives for sellers to use the program although buyers hate it because it cost them than if the seller didn't use it.
If you pay for import fees at check out, you will not (or should not) be charged again if you have to pick up your item at the post office.
From ebay.com
"The Global Shipping Program also makes it easier for buyers in other countries to purchase items from US sellers. Buyers can see the shipping and import charges before purchasing, and can also track their item globally. Find out more about buying an item through the Global Shipping Program."
By the way, before this program was implemented, many buyers who bought from other countries complained when they discovered they had to pay import fees after they had already paid postage to the seller. Now instead of being surprised later on, you know before bidding, what the import fees will be and can make a decision whether or not to buy the item.
Once you bid/buy the item, you have agreed to the import fees shown.
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Non payers should get unpaid item strikes and be added to block bidders lists. Period.