In the movie, one of the crashers tells the father of the bride or groom, that he is the son of the man's DEAD sister. And no, I don't know if that was bought, because that's when that clip ended. But it is far more than just INPLAUSABLE, for a man to not know the children of his sister and whether or not they were invited.
Any girl, who is bamboozled by a line, was looking to to be bamboozled. It has little to do with the guy and his "game".
From where I stand all women are always looking for something. Why? Because they want everything. The key is to find out what they want. When you do, you're in like Flynn. It's much more than a line, it's a dialog. As long as there's dialog, there's always an opportunity.