Don't I know that! There are always going to be a few customers that you really don't want in your shop. Fortunately, I've only run into 3 in the last 20 years. I try to keep in mind the old adage that a happy customer will tell a few friends about their good experiences with you, but an unhappy customer will tell 20 or 30 about your "terrible" business. It pays to make sure you have no unhappy customers. The 3 "bad" customers I had, I quietly took the aside and politely suggested that they would probably be better served by another. In fact, in each case I purposely lost all of the money in the transaction, so they would not feel it necessary to talk too badly about my business.

You have to be real careful in today's world of the internet, because an unhappy customer may tell a few thousand people how bad their experience was.