In the movie, while in the Burj Khalif hotel during the con they are playing with the switching of the rooms, Simon Pegg's character had a fake right hand so his real right hand can steal the diamonds, thereby leaving his left hand to do the serving. In Middle-East cultures the left hand is used for bodily tasks like toilet paper and such. It is considered extremely rude (Not to mention unsanitary) to reach for food, serve food or even shake hands with your left hand. This would be just a small slip up except it would have been picked up quickly by anybody familiar with the culture.