The 70-200 EX has been around for a few years, so there's a possibility that compatibility problems with the latest EOS bodies may already be lurking around the first batches of that lens. Of course if you're buying a brand new lens from the latest production batches today, chances are that it will work. Then again, it's always prudent to test the lens/body combination on the spot.
That's quite a good price for that lens. I still recall it costing in the neighborhood of HKD5000 when it was introduced not too long ago. Anyway, now I know how to identify you around CLK!!