1. I need time to thing about this.
This isn't a lie- but it isn't the truth either. When someone says this to you it means he or she is still looking at other candidates and you're not their first choice. If someone says this to you, pass on any re-interview offers, opps. to lower your rate as a consultant or re-pitching your services. It is a waste of your time.
2. I need to know I'm your only, or most important, client.
All clients are important. How you answer this will help people determine if you're a liar. So, if you don't want to fall on other people's BS meter- be honest. Try saying something like, "Our clients are like children. We don't have favorites and try to help each one grow. However, some children need special attention. Our special child pays us double what you're paying now for this service. Is this something you're willing to do?"
3. Talking too much. People who tend to over explain things tend to stretch their capabilities. Direct, short answers usually are an indicator of someone telling the truth. Always keep this in mind in every sense of your personal and business dealings.