Are there customs fees with importing airguns? Where can I find out the rate?

I have read that customs isn't always consistent on duty fees.
More like UPS isn't. My $807 scope I originally paid an additional $260 in fees on. That didn't seem right so I ended up calling UPS and asking why. Well Krale had the X50 listed as "made in China" which tacked on an additional 25% tax. Sent them a link to Falcons X50 product page which distinctly says "Made in Japan" and they processed a $200 refund.
 
Bear-of-Grayling figured it out about a year ago, in 1971 CBI (Caribbean Basin Initiative) was established so Import Duty Fees could be collected by USA. Since the Netherland Antilles, in the Caribbean, are under Dutch (Netherlands) administration we are charged duty fees buying from Krales in the Netherlands, that is, anything over $800. WM