You should be fine buying equipment from other locations, such as China, but there are a few things to remember. First of all, you need to keep in mind that your warranty will be void if you use the lens in another country (more specifically if it breaks in another country), which is one reason why I'd buy all my "serious" glass (mainly lenses that cost more than a few hundred dollars), in Canada, or wherever you live. You also have to keep in mind common sense, generally if a deal is too good to be true, it's probably a scam.
Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories
"There are no rules for good photographs, there are only good photographs."
- Ansel Adams