You may need to make a call or two to cancel your plans for the evening, and your first impulse may be to lie about it, just so that no one's feelings are hurt. But if you're canceling because an exciting offer has come along: the kind that you really can't refuse: why not be honest about it? After all, if they're your friends, then they know you, and if they know you, they'll understand. And isn't it better to be honest?