We have used Sixt a few times in SXM. A representative holding a Sixt sign would be outside of the arrivals hall. We did not use them in March but did notice they had a booth inside of the terminal at the end beside the exit that is on your right as you leave the terminal. I am not sure it is always "manned' but there is a phone you can use to call them. We never had any problems with Sixt. The cars were always quite new and we often received a free upgrade. The only reason we changed was price. In March and again for our upcoming trip in July we are using Triple A.