I also have extensive experience with Athens taxi drivers. In my experience, about a third of them are cheats, about a third are honest but couldn't care less about service and don't know the city well, and a third are pleasant, honest, and competent. I'm talking about the official, metered taxis: there are also unlicensed "gypsy" taxi drivers who will approach you in Piraeus and other touristed spots. These are to be avoided like the plague.

One of the worst things about Athens taxis is that so many of them are in disgusting shape: broken air conditioning, filthy interiors, and sometimes, astonishingly and outrageously, with seatbelts that are broken or deliberately disabled.

You're much less likely to have a problem with a taxi called for you by your hotel, though this costs a few Euros extra.

Outside of Athens taxis and their drivers tend to be much better.