Customer is always right, no matter what. Do everything you can to let the customer leave with a smile on their face, satisfied with their experience. Don't let you anger take over, just be calm no matter how stressed you are. Similar to how they don't know what's going on in your life, you don't know what's going on in theirs. Greet the customers when they walk in to make them feel comfortable and let them know that you will help them with anything. Help them from the minute they walk in to the minute they walk out.