http://www.cbsa-asfc.gc.ca/import/postal-postale/duty-droits-eng.html
You will also be charged sales tax, up to 15% of the value of the item and an border clearance fee to the shipper ($10 if it's Canada Post who delivers)
For quality of the product and reliability of the seller look at the feedback numbers, read the feedback for repeated problems, and consider the Detailed Seller Ratings.
Feedback that drops below 98% is pretty poor. Below 97%- run.
If there is anything wrong with the item on arrival, it may be necessary to return it to the seller with Confirmation of Delivery or to write it all off as a bad deal.