I agree that generally tipping is not needed, rounding up is typical, and it avoids making change, whether at a taxi or restaurant. Hotel Maids? I do not recall ever leaving a tip, in Greece, elsewhere in Europe, Mexico, or even in the US.
For tour guides, you are obviously a tourist at that point and many expect a tip, though again, not mandatory, a euro or two would be fine.
It is true though that if you eat in the more touristed places, the staff may expect or even hustle you for a tip. A parallel example recently was in Berlin, bill came, all in German, except for the phrase "Service Not Included" in English, and circled in ink by the waiter. I am sure that the locals tipped as I did (if they tipped) by rounding up, maybe an extra euro or two...though I am sure the waiter would have loved me leaving 10 to 20%. Not being mean, just not being played.