It depends on your driver. I got conned in Athens too - the driver had a little button beside his gear stick that would add 1 Euro everytime he hit it. He pressed that button a lot, and the fare was around 40 Euros. I have him a 50, and he did a trick with his hand to produce a 5 Euro note that he said I have him, trying to get yet more money out of me.

Honestly, as a tourist I absolutely fucking hate taking taxis :-/