You're always going to deal with customers who are demanding and/or in a bad mood. The way to not get bad remarks is to not respond negatively. Keep a smile on your face, answer their questions, listen to their complaints, serve them, then tell them to have a good day. I know easier said than done, but if you do it enough it will come natural. My first couple of weeks working for Kroger I dealt with some really mean and demanding customers. It got to me! I didn't think I would be able to handle it. As the weeks went by I learnt that if I just smiled and did my job, the bad comments stopped and the good comments started coming. When you are taking care of a demanding customer the other customers recognize how you dealt with the situation and will give compliments about it. Don't let the bad ones get to you. Try to learn from them instead.