I was reminded by this Flyertalk thread that Sixt still comps status — rental car status based on airline or hotel status — and history holds true, there isn’t even any verification of your actual airline or hotel elite status.
When I got my Sixt Platinum card (based on real status, but no proof submitted), it was valid for 4 or 5 years.
I’ve used this about five years now, did it when I was a 1K and it came through fine. I continue to get mailings (even here in the USA) so I assume I am still member.
But, when I book rentals, I do NOT find that I get the best rates. Especially on the weekends, when the weekend rate is better (which starts on Thursday 12:00 for SIXT and end at 12:00 on Monday)
What it DOES get me, is easy check-in and MAJOR preference and perks at the check-in desk. (you gotta love Caste societies) Flash the Platinum card (just so they can confirm your NUMBER is in the system of course) and find that your BMW 1 series is now an E200CDI or BMW 330TdI or something like that. I’ve even managed the mythical 99EURO SL550 for a weekend rental. So, the card does SOMETHING, but not a big discount IMHO.