I currently purchase a number of items through eBay and to date have never had to pay duties. Most of my purchases are between $200 and $500 US.
On the other hand a friend of my recently purchased a framed painting for $3500 US and to this day, every purchase she has made since that purchase, including a number of small purchases has attracted Customs duty.
It would seem that once they have your name you'll be saddled with duties.

Mark