We use tag questions to try to get another person to commit to doing something that we want him to do. Salespeople frequently use them.
Examples: You're going to get this done by tomorrow, aren't you? You're not going to change your mind on this, are you? You like going out with me, don't you? You like this color, don't you? You'll buy this tomorrow, won't you?
Using tag questions gives people more control. This makes listeners feel weaker emotionally when they hear them. Many listeners feel manipulated when people use tag questions on them.