Terrible experience. The only positive thing I have to say about it is that the vehicle drove well and fit our needs. The customer service was horrible. The main desk associate was rude and treated us as if we were going to steal the vehicle. The downstairs associate wasn't even at her post when we got there, despite the upstairs person having called down about the vehicle we were to be assigned. We waited 15 minutes for her to return, then another 20 for the car. When we asked her to walk 40 feet over to the car with us, so she could record any damage we observed (and save us a minute or two, since we'd already been there for nearly an hour) she refused. Another associate ended up doing it and I took my own photos of existing body damage to be sure we had documentation.
We had no credit/debit card issues and no issues with expecting one make of vehicle and receiving another. We needed a particular size and that's what we got, so I cannot speak to these areas where other reviewers seem to have had trouble.
I called the agency three times before I was able to speak with the manager, who was nice enough, but gave no answers as to why it took so long to produce the vehicle we had reserved or where her staff might have been for so long. She offered a voucher for our trouble, but I'll have to think long and hard about whether we'll ever use it, as we didn't choose Sixt to begin with. One bright spot I will mention - the gentleman who checked in our vehicle when we returned was very pleasant and seemed to be on top of things. I wish that made up for the rest. We have had good luck with Hotwire purchases in the past, because we have always been with one of the main three car rental agencies. This was definitely a gamble we came out on the short end of.