I have always found dolmus drivers to be meticulous in the matter of charging. If you paywhen you get off then I bet you'll be charged the appropriate price. For example, last month we caught a dolmus from Marmaris otogar and asked for "Ataturk" (i.e. his statue on the seafront) and paid a two lira each (for two of us). When we got near the seafront we got stuck in a traffic light jam, and since we were only a hundred yards from the front and the door was open we jumped off. As we walked past the stationary dolmus the driver honked the horn and shouted at us to come over. I thought we might be told off for jumping off without notice. On the contrary, the driver wanted to give me one lira back because we hadn't done the full journey.
There might be lots of rip-offs inTurkey but i have never experienced one on the dolmus. Perhaps I have been lucky?