I use Sixt service many times. First of all. During high Season there could be some delay as other company too. There will a queue due all flights arriving at the same day and time.. There are always customer making it difficult and putting other to wait. Overall we are happy using Sixt as we do like the car they rent and the brandings. We where always getting extra service or greater nicer car replaced if any delay or issues. With no extra. We had as well car rented where we had to change trop off destination or requested extra additional days rental. the service is good ,cars are always ok. As mentioned, if there are more stress days or issues on car, .looking other Renting on the same place do have same issues, maybe you are in Summertime high season or other reason where everyone want to have a car to leave for holiday. For the service like web or Apps to rent ordering changes are usually working . We had one time issues where none was working , we needed to extend the rental,the web was not mentioning the option, the app did not had the option either to change , then the support was closed on Sunday, but we could contact by What's up and got all set. Of course we could now argue that it could have been done in a normal way. We think that it was ok as at the end we got what we requested. The Sixt support in Germany was the best one , you could contact them no matter what country you rent the car and they take care of you. For the prices, It is not the cheapest but we tried other cheaper company. The difference ? Less car selection, less options,. Some other have newer cars with less milage guarantee. But we never had cars from Sixt with high milage too. The small damages you may have on cars are all noted before you use the car, we never had any problems that damage was been notice while we used it. This to say that damages are not invented once you dropped of. On the higher expensif Brand model especially BMW , cars are fully equipped with many many extra. On middle model the options on cars are those you need mostly.