When picking up the car, many things were not communicated clearly, and there were issues contacting the rental company. We picked up the car at Frankfurt Airport and were told we had to pay even though we had already paid in full in our home country. The representative said they couldn't find the payment on the system. After calling the rental company and sending some pictures, the issue was resolved. They mentioned a fee of five euros per day for additional drivers and a cross-border fee, which was acceptable. However, when returning the car, they said the payment was incomplete. Besides the additional driver and cross-border fees, there was a 21% tax, totaling 389 euros. After contacting the rental company again, we finally paid 329 euros. This process was quite unreliable, even if the rental price was relatively cheap. Can't the rental company standardize their operational procedures?