What is a Bait and Switch?
Luring in someone with false pretenses, which might include: Going over to talk to a person in order to get to know them for your friend when in fact you're getting to know them for yourself, leading someone into heavy detailed-flirty conversation only to announce halfway through that they want to know about your friend, or essentially any event which leads to one party getting to know someone in order to attract personal gain at the expense of another party.
Now while the bait and switch stings, it is a necessary part of life which helps you develop a more secure and resolute flirting style. You learn to adapt to people you talk to with out even realizing it, but be wary, because if you happen to be interested in someone and are off your game, you might be passed by.
How do you cope?
There are many fish out their in the sea and while your crush might be the most fabulous person in the room, chances are that they are not the most fabulous person in the world. A party is just a party and a person is just a person. Don't put people up on pedestals when you first meet them or really at all, because that allows someone to have control over your emotions in a way that they shouldn't have, because your emotions should be yours alone.
If you find yourself at the negative end of the Bait and Switch don't worry, because as I have said, there are many other fish in the sea, but as with everything you need to notice trends in your life. If a friend constantly says that she is luring a guy to you, but then steals him for herself. You have a problem. Address it and move forward. If you notice that people are constantly attracted to your other friends then try to figure out what they have that you don't. I'm not advocating changing yourself, please G-d don't, because you're you for a reason. What I'm saying is that maybe you should step out of your normal party/meeting people comfort zone and try other tactics, which might have a more positive effect.