Alright, I need to step in to correct a few things.
First, the comment about not having to pay GST if its for business/resale. Not true. You still need to pay the GST when it arrives. However, if you have a BN, you can claim the GST back. The government will know you're up to no good though since your not collecting any GST, and are only claiming GST back.
Second, the $5 the post office charges is NOT for collecting GST/PST, its for duty brokerage.
Third, FEDEX DOES NOT charge a duty brokerage fee. That fee is already included in their cost of shipping the package.