A group that I sailed with last year went with Terry and had a great experience. Definately do this or a ship sponsored excursion there. They are VERY aggressive. We took a cab to a beach and the hawkers kept coming back over and over even though we were the only few people on the beach. There aren't many sandy beaches there, so if that's what you want be sure to do your homework!
Could I ask which beach you went to? How much was your taxi? Did your driver stay with you? How did you find him? I am going on the Pearl on March 13th. I want to go to Playa Rincon. Any help would be great.