I would call for appointment of a waiting list, then you would be ahead of the walk-ins. If you don't have a burner, then it is the only reason I would walk in. My experience is they would tell me to come in regardless busy or not (most of the time anyway). Very few would turn the customers away on the phone. They would do their best to accommodate, but they know most guys would not walk out. With GDS, you should set aside an extra 30 minutes so avoiding disappointment.