US Buyer Here. Help me understand

I haven’t bought anything internationally since before the tariff change kicked in. In theory, I understand how much more a US buyer is SUPPOSED to pay for international goods based on the Tariff for the manufacturing company. However, I keep hearing these horror stories of people getting charged an absurd amount by UPS after having already paid the tariffs/duties to their proxy.

I’m trying to bid on some items on Yahoo Japan Auctions, as well as order an item from Carousell, but I’m fearful of getting that crazy bill from UPS after it’s too late to back out.

I apologize for my misunderstanding if any, but I figured I’d get real testimony from other buyers.

Thanks!