Just imagine if everybody did what you're doing.

Pilots do their fuel/weight & balance calcuations based on what is entered into the system at check-in. If ONE person smuggles through some extra kilos it's probably within allowable margins. If lots of people do it you could end up with an aircraft that's too heavy to take off, or you could run out of fuel before you reach your destination.

I hope this thread is going to make the airport authorities aware of what's going on, and that they'll put a stop to it.