US/Canada Customs Fees

Thanks for the responses. Actually this is a specific topic that I have not seen discussed on this forum. I will restate the question.
I am asking about carrying and declaring used, private sale items across the border from Canada to US (ie in the back seat of my car). If I purchased a used audiophile item with value of US$4000 (made in Canada), what fees if any should I expect to pay at the border crossing? I guess this question is directed at those of us who live near the border. Thanks again.

I just read on US Customs website that they will collect a duty based on declared value. First $400 is exempt. The next $1000 (up to $1400) will have a duty of 1.5%. Anything over $1400 will have a different rate depending on location. The exemption can be doubled to $800 if you travel with a US buddy. God this is a great country.
Any other first hand experiences?

The sale did not go through so I don't have first hand experience.
Per my 6/13 post there is a duty based on declared value (with receipt) over $400, independent of NAFTA. However I do not understand if this applies to private sales of used equipment. There may or may not be an additional fee if the equipment was produced in a non-NAFTA country, I still don't know for certain. I would hate to be surprised with an extra duty at the border, therefore I will not be purchasing non-NAFTA items from Canada until this is known to me.