I just returned from Greece, and I just want to make people aware of what seems to be a relatively common scam used by some taxi drivers.
When I arrived in Greece, I decided to take a taxi since I wasn't entirely sure where my hotel was located in relation to Syntagma Square (where the airport bus drops you off). I went to the taxi line and got in the first cab that was in the line.
I was told by Airport Information staff that the ride from the airport into the city would be 35 euros. However, once the driver had my bag in the trunk and we were on the highway and he told me it was actually 40 euros for an "airport station pickup." That was bad enough but it got worse when we got to the hotel. I gave him a 50 euro note, he turned toward his door and held out a 10 euro bill to me and said "you gave me a 10, it looks very similar to the 50." Without thinking twice, I very stupidly gave him another 50 to which he gave me the 10. Unfortunately, it didn't occur to me to ask for a receipt. When I got to the hotel, I realized what had happened. He had ripped me off terribly. Needless to say, I was extremely angry at myself and the driver.
Please be aware of this problem and don't let it happen to you. I would recommend paying the driver in 10s and 20s to make sure they can't rip you off.