Hertz's overall service was terrible. We had to wait in line for more than half an hour at Frankfurt Airport to pick up the car, only to find out that their store's computer system and POS machine were both down. They said they needed to do a pre-authorization over the phone. After showing them three cards, they finally said it was successful. However, we received bank messages showing pre-authorization on all three cards. They provided incorrect parking information, making us search for the car for quite some time, and eventually, we got help from staff from another rental company to find the car on an upper level. When returning the car at the Frankfurt city center location, I requested a receipt and was told to come back the next day. When I went the next day, they said they would check immediately and to come back in 20 minutes. After waiting 20 minutes and returning, the counter staff had already left. A neighboring rental company employee said he received an emergency call and had to leave. We had to go back a third day and were presented with a bill over 600 euros higher than our booking. When we discussed the incorrect charges with the staff, they told us that they billed according to the computer records and advised us to call customer service. We had to fly back to our home country that day, so we could only handle the issue after returning. Overall, this was a terrible car rental experience.