We have just returned from 17 days touring Northern Greece & just wanted to mention the excellent car rental company we used. Instead of going through an anonymous online broker we found a super local family owned company & cannot fault them for service & price. They gave us an all-in price (subject to usual deductible excess) & at no point tried to sell us any add-ons or extras. A small advance deposit secured the car many months ago & even that would have been returnable had we been forced to cancel within a few days of travel.
I was able to make arrangements direct with the owner, Nicolas, & we got exactly the car we requested, in excellent condition & arranged a "pick it up full return it full fuel" policy so we could get straight on our journey. We mere met at the airport arrivals hall & the paperwork was completed with minimum fuss with a very personal feel to the whole transaction.
We later discovered that a friend of our who lives in Athens has used Athens Car Rental many times & congratulated us on our choice. Check out their website - their prices are hard to beat & service is totally reliable.