The action (generally illegal) of advertising goods which are an apparent bargain, with the intention of substituting inferior or more expensive goods. – Oxford.

Creating a deal that is cheap and easy and then talking the customer into going for something more expensive. The cheaper item is to get them in the door, in front of you, so that you can then talk them into a more expensive item.
Like the car at the front of the car sales, a cheap model to catch the eye of people passing by, they go in hoping to get a bargain, but once inside the fence they are talked into buying a more expensive car.

Although this can be considered illegal it happens all the time and the customer is either pleased to get away from the salesperson or they are so happy with their new expensive purchase and are trying to figure out how they are going to pay for it with their meager wages that they generally forget the salespersons technique.
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A manipulator could use this technique to show you or offer you something that appeals to you, but with friends and careful manipulation, peer pressure, guilt, etc, can then lead you to something you really didn’t want and was out of your range but next thing you know you are caught up in the while thing and have signed the dotted line or agreed to it.
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I have seen this where a person who doesn’t like to go out much goes to a dinner after some pressure from friends/workmates, and then after a few drinks, lots of laughter, caught up in the fun, some peer pressure to have fun and be with friends, she goes to a party (which she basically never does), gets drunk, sleeps with a man who was just using her and regrets herself, her life and everything the next day.
Say, “No!” from the start and you cannot be led from the bait to something bigger and what you will regret.
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When you go into something, remain stubborn, I love doing this.
Just say, “No!”, then say it again and again,

No matter how attractive the deal appears to be (know that it isn’t and that somewhere is a catch) that goes beyond the bait say a firm healthy, “No!” and you will be amazed at how good this feels, and how powerful you feel saying, “No!” over and over again, even to family and friends.

If you have doubts later don’t worry about it, forget it, because there is always something else somewhere, bargains happen all the time, this is the way of buying and selling, its no problem.
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When people offer you something ask yourself, “Is this bait?” and if your instincts say yes, then prepare to say, “No!”
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If your friends act sad because you don’t buy it, or they say, “Oh, you don’t trust me!”
Know that your “friend” is baiting you, because real friends don’t make you feel guilty.
Be strong, no one wants to be a sucker.
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Bait and Switch in charitable situations:
You may be known for your soft heart, your giving nature, for your kindness.
Someone comes to you for some money, or a small amount of food, but then they tell a sad story about the hard times they are going through, how tough life is, and you find that the small donation that you are making to this person is not enough (according to their sad story) and you eagerly buy them more or give them more, the next thing you know you are short of money.

They gave you the bait which you thought that you could easily afford and then sprung the trap to get much more out of you leaving you short of cash and them walking away smiling.