I have Platinum and received no upgrade today. Counter rep said he only had high end cars - so a standard car is what I reserved and a standard car is what I got (Toyota Corolla). He refused to give me anything higher (again stating he had no full size and wouldn't go higher). I do not have the 10 rentals required for upgrades (although he didn't mention that as being a reason). Frustrating but not unexpected. It's why Sixt is not my preferred car rental company.