My wife and I have visited Sea Ranch 4 times now and we love it. We've tried a few of the rental agencies, and just got home from a very bad experience with one particular agency. We rented through:
They were very unpleasant, and more importantly, the house was in a state of disrepair. The Washer-Dryer was pre-historic, and unsurprisingly didn't work. The stereo was broken, as was one of the heaters, and the fireplace. When we mentioned this to the agency they made no apologies or attempts to right the situation. Instead the suggested we should just rent from some other agency next time.
FYI, the house was the "Creekside", which would've been a nice house otherwise.
As an aside, we used http://www.searanchrentals the other 3 times and they were very pleasant and accomodating. It felt like they took a lot more pride in the properties they managed.