When we were in Barcelona last summer, we told a woman cab driver we wanted to go to the cruise ship terminal from our hotel and even pointed to it on a map. She drove around in circles retracing her tracks a few times. She "seemed" lost. We had been on a hop-on-hop-off and had seen the terminal area, so had a good idea of where we had to go. Long story short, she waaaay over-charged us. This was the only fly in the ointment to the beginning of a memorable cruise. I saw on another forum, the solution to such foolishness--take a photo of the driver and the license plate of the cab before you get in it! Doing that, I doubt if that scam would happen again!
We were in Prague - wanted to take taxi to train station. Actually we could have walked or taken the bus but since we had luggage and my foot was bothering me, we opted for the cab which would have cost about US$3. Our Airbnb host arranged it for us, so we thought we were okay. I guess driver was not happy about the short trip and drove us around. We had been in the city for 4 days so we sort knew the area. When we told him we knew he was doing, he pretended not to understand us. We got to train station okay, on time, etc. But we were not happy. We had set aside enough Czech currency for the cab ride and for using the pay toilets at the train station in case we needed it. We sort of short changed him because that was all we had which was about US$5 and the fare was a bit more. So we didn't pay what he wanted but he had "taken us on a ride". When he protested, we just told him that what he did was wrong and that was all the money we had. This was the only "bad" experience we had during our trip other than leaving our pack back with our iPad in it at the Berlin train station (which we got back 6 weeks later). Will take photo of driver and license plate - good idea!
So you paid $5 for a ride that you were told would cost $3. Geez ....
I think Dee's giving us an example of how to handle the situation. If you do have a solid resource telling you what fare to expect, and you are certain they took you on an unnecessary detour, then give them the money you were prepared to spend instead of what they ask for.
My fare turned out to be 20 euros for what should have been a 10-15 minute ride.