I'm running into this myself right now as well. It appears that false damage claims are core to Sixt's business model.

I rented from GVA in Feb and am now dealing with a false claim of ~$3k in damage from that.

I rented from MSP this week and was given a beat-to-hell Highlander with 7 items already noted on the slip. This morning, I received a damage report from Sixt claiming that I time traveled and caused two of those 7 pre-existing items.