I reserved from sixt when I went to Mia a few weeks ago. National was more expensive than everywhere else so I decided to try something new.
They wouldn't give me any upgrade. Just the Camry I reserved. Then the agent asks if my wife will be driving. I say yes but you don't need to add her on since she's my wife. He says ok just needs to see her license.
In the end the bill with the extra driver and other fees was same as national. I asked the guy about the starwood benefits with sixt, he had no idea, I told him if he can't upgrade me I'll just go use my executive club over there. And that's what I did. Sixt charged my card and emailed me an invoice for one day, I emailed them saying I never rented and the refunded me.
Not a pleasant experience. That agent was a jerk tacking on fees, and because of him I'll never use sixt again.