I have a question regarding Sixt upgrades. I am a Sixt Platinum member which I received through my World Elite Mastercard. However, I already met the Platinum card requirements based on the number of rentals I have placed with Sixt. In addition, I sometimes book through my corporate code as well.

I would say that for around 90% of my rentals I get a free upgrade but I'm wondering why in some cases I don't. For example, today I was asked if I wanted to upgrade but at a cost. Initially they quoted me at around $150 to $200 extra a day but then they brought it down to $20 a day.

Is it mostly an availability thing?