what is the difference between booking the car online and in the office personal?
Online the prices are lower. At the car rental desk you will almost alway pay more then in advance online.
Is it possible to pick up the vehicle in the City centre of Athens and drop it off at the Airport of Thessaloniki?
If you intend to drop off the vehicle in a different location from the pick up location, then tick the box “Return to a different location”. If then no cars are displayed at STEP2, then one way is not permitted between these locations.
For one way rentals sometimes it can be a fee. This is almost always included in the total rental rate and payable at the desk on arrival.