Fake bindings? Really? Bindings aren't made out of gold and diamonds... they're mostly plastic and aluminium/steel. The cost to make a "fake" would rival making a real one.
The only thing you should be worried about is that they are actually 2011 Burton Cartels and not old Cartels or some other Burton binding. If you know what they look like, there is no way you can get ripped off.
and BTW, are they used? Here's some for $160 new Burton Men's Cartel Binding (2011) - Sport Chalet