The Zakynthos airport is likely building various rental kiosks. They wait with signs at the airport exit, which is convenient. Their current store is just to the left of the airport exit with a clearly marked sign. The process is convenient, although I'm slightly disappointed I couldn't choose the car myself. For mountain roads, a powerful car is better.

Very slow. Clearly had cars available but didn't give one. The car was also extremely old.

No airport pickup, has to walk 5 minutes to the office. Counter staff was rude. Car was nothing like the one I saw in the pictures. The car condition was terrible, old and dirty with engine sounds. Upon returning the car, they knew exactly where to look for to find an odd chip in the paint job underneath the car, and charged me for the damage. I would not recommend this company one bit even if the rental is free.