When dealing with customers and clients, there are some phrases that are universally annoying.  Using them makes customer relations more difficult; avoiding them will improve the level of service you provide.  Here are a few:

• "That's not correct."
  Don't ever tell a customer or client they are wrong.  With many people, it will cause their blood to boil.  Here are some examples of rephrasing it:

  "Obviously, I did not make myself clear."
  "That may be the case; I simply have never heard it."
  "That is an unusual approach for a claims adjuster; let me do some checking and see what he is talking about."
  

You can accomplish your goals without ever telling someone they are wrong.  Generally, it is worth the additional effort required to rephrase it.

• "We can't do that."
  The way to tactfully skirt this one will depend on the circumstances; but, here are some samples.

  "We've never been able to do that; but, let me see how we can help you solve this."
  "I think I understand what you are requesting; we are just not set up to invoice you on a daily basis. Let's see, how else could we work this out?"
  "I wish the industry were set up to do that; unfortunately, I do not know an insurance company that permits that."
  

You never want to make them feel as if you are saying a flat "No."

• "Let me tell you what you have to do."
  Many people do not like to be told what to do. Try this: "In the past, my clients have found this works." Then you proceed to tell them what to do.

Today, many people are stressed out and few have time to spare.  Often they feel they have been bruised and abused by the customer service representatives they deal with in other industries.  As a result, they are very sensitive to being told they are wrong or what they can and cannot do.

With a little sensitivity and some experience at rephrasing, you can project a helpful, problem-solving attitude.  It will distinguish you from the competition and many will appreciate it.