How can I let shoppers know that they're already paying taxes and duties at checkout?

The BorderGuru App quotes both shipping and import fees to the customer, and it breaks the split between these two down when showing the quote to the customer. They can see the tax & duty portion of their payment clearly broken out, so they know this payment won't be requested of them when they receive the shipment anymore.

This also means that, even if the biggest portion of the BorderGuru quote is related to taxes & duties (typically the case with small, high-value items like jewelry, etc.), customers will still be able to recognize the great shipping rate they are getting. 

In general, we recommend adding information about international shipping to your FAQs and the terms and conditions of your store. In this section, you can explain how BorderGuru already calculates and collects all import fees, including taxes and duties, at checkout already.

In our experience, sellers can also increase the conversion rate of their international visitors if they offer information about international shipping in a subsection of the landing page, or another section of the shop that is easily visible.