It is important to remember that there will be customers that come into your establishment were already having a bad day prior to even entering your establishment. Any negative behavior they are exhibiting is not because of you. Remember to be kind, courteous, and to continue to provide them excellent service. Being apologetic to whatever the issue might be is very important. Try to ensure that you are sympathetic to their feelings and empathetic to whatever they might be dealing wit. The customer wants too feel as though they are being taken care of and are being truly provided for in every way possible.