I think that 425 euros is about right. No need to tip for fuel, entrance fees etc.

Also, keep in mind, no matter how this "private tour guide" advertised his services, he is NOT actually a licensed tour guide, he is simply a taxi driver. He will drive you to Epidaurus, Mycenae, ancient Corinth etc. He can give you a few anecodotes about these ancient sites and give you a map, and wait for you at the entrance. BUT He is not allowed to accompany you onto the sites, nor into the Museums in Nafplio or into its Palamidi Fortress ... onsite you will be strictly on your own, without a site guide. He has not completed any studies about the sites or GReek history/archeoology etc and so has no guide license. You are hiring a taxi. So think about taxi tipping -- plus for any kindnesses along the way.

Janet, your point is well-taken, but this is not just a "taxi driver". This woman is a tour guide my girlfriend's parents used a few years ago in Athens. Her parents travel A LOT and use tour guide services around the world. They claim this Greek tour guide was BY FAR the best they've ever used anywhere.

You should tip for the guide's fee only. You don't tip the entrance fee folk at the local museum at home or the gas station attendant etc. You want to be generous 15% max and it'd better be special. Do you tip the secretary in your business for doing her job...no. Service industry is different but remember,she is getting a salary. Your family has used her before and like her...ask her up front what she personally will be paid for the tour. Figure the tip out from there. If she deflates her commission well in good conscience you did the best you could. The driver, if a separate person, should also receive some small tip. Seems to me only Americans stress about tipping (really we are a very fair group of folk). Cruise lines now include tipping on their day to day charges (can be declined) because many Europeans and Asians don't have a culture of tipping. Good for you for trying to be a Good Guy (Gal):)