Some sellers will pre-pay the duty, and in doing so they might provide an HS code that is a lower rate and assumes risk of fraud. That's been my experience buying parts internationally on eBay recently. Some of the paperwork was fudged... but not my doing.
For items where the seller hasn't gone through that hassle, DHL tends to send me an email in advance of receiving the item to pay the tariff and their fee for handling it, FedEx however will send this collection email 2 weeks after it's received just when you're starting to think you were in the clear of it. Something to be aware of.