What your employees do not say is as important as what they do say. You have to develop the ability to listen to what they are not saying and dig through that to get to the truth. Otherwise you will have the false perception that you are doing fine - right up to the minute you are fired and replaced by someone who can be effective. So
Listen To What They Are Not Saying.
The best way to find out whether your customers are satisfied is to ask them. What you ask and how you ask are important. However, the most important thing is what you do with their answers. Read
Customer Satisfaction Surveys to learn how to do a customer satisfaction survey that works.