Customs Duty on iMacs coming into Canada?

The Refurb'ed iMac I recently bought was purchased through the Apple Canada website but, it was shipped from California. I've just received, a statement from Fedex that indicates that I owe them $31.08 for customs duty.

Since when are the purchasers responsible for paying the customs duty?

If I'm responsible for paying said duty, I'll pay Fedex the specified amount after I bill them - and get paid, for the 2 days that I waited at home for delivery of the aforementioned computer.

My time has value too!

Maybe we can split the difference ...they can drop the $31.08 and I'll only charge them for 14 hours of wasted, unproductive time, rather than 16.