A friend of mine used them a couple of weeks ago it was her and 2 kids and because they agreed to go in a car rather than a mini bus he charged them the price for 2 people. He always answers emails promptly and speaks/writes good English.
I suspect they stop off at cafes to give them business, perhaps there is some financial incentive too but I don't know that. There are quite a few cafes that have opened up about half way between Dalaman and Marmaris. One taxi driver wanted to stop for a coffee - turns out it was his cousins place!
Have a great holiday.