I am considering flying into Thessaloniki, renting a car and driving to FYR Macedonia (Skopje), returning it back to Thessaloniki. Do rental companies allow this by default? Is there anything special I need to look into in the rental agreement? How does the insurance work in this case?
It is technically possible but practically virtually impossible.
There are so many issues you would face:
- finding a car rental that would allow you to do this
- getting legal permission from a car rental to drive across the border
- obtaining insurance that is valid in both countries
- receiving clearance from both customs
Many car rental companies won't even let you take your car to a Greek island, not to say to another country.
Your only option is to leave a car in Greece, cross a border by bus/taxi/etc and rent another car in Macedonia.
I continued to research after my previous discouraging comment, and it is difficult but not impossible. Avis will allow, if the reservation is made directly with them (there is an email at that link), and an additional insurance fee of over 100 Euros, depending on car class. Also, renter must have either American Express or Diners Club.
Economycarrentals.com, which you can see recommended on other sites, is now a No. Thrifty, No. Enterprise theoretically can be arranged, but many surcharges including loss of unlimited mileage.