Hi, I am canadian and buy and ship to the US pretty often.
First of all, if you are afraid about the buyer saying that he has not received the item, just ask for a delivery confirmation and/or tracking number.
UPS can track your item but for the buyer, he will go
when he gets his duty fees (pretty expensive with UPS). I never ask UPS for shipping.
USPS, the worst he can pay for duty fees is 5$ + 14%tx. If you lower the shipping value of the item, he or she will save on duty fees except if you do a claim, the amount you put on the duty sheet is the amount you will be aloud to receive (ex. declare 10$ and the buggy is worth 500$, if they lose it...10$ in your pocket). But don't worry, I have never lost an item in over 250+ transaction US to Canada.
Hope this help.
My ebay username is falconcg
My club website is www.rcottawa.com