Think of examples of service that you've received that made you very dissatisfied. Most people when tasked with this challenge will admit that those circumstances that incensed them the most were the result of failure of service providers to live up to expectations, and worse yet, then not caring that they didn't do so.
In dealing with your clients, how much time do you spend correcting service failures or customer dissatisfaction experiences that were purely related to the customer expecting one thing, and your team delivering something else? I would expect that many of these instances are the result of mis-matched expectations. If that is the case, how do you prevent it from happening in the future?
The best way to prevent this failure of expectations is to define your service expectations very clearly, communicate them clearly and regularly to your customers, and then deliver beyond those expectations! This would be the definition of a 'WOW' service. People don't like surprises of the negative kind. If you encounter too many episodes of failed expectations, revisit what you're communicating to your customers, how you're communicating it, and make sure that the message is clear, constantly available and achievable by your team. In addition, make certain that you communicate those expectations at all times to your team, to ensure that they deliver beyond those expectations.
Be proactive: communicate your service expectations clearly!