Do an odometer reading when you first arrive at the valet's location. The best way to do this is by snapping a photo of the odometer with your smartphone. (While you're at it, snap a photo of your fuel level too. And then snap a photo of the valet's face and name tag.)
After you get it back, if the mileage is excessive, then you should negotiate compensation with the valet manager. (And the valet manager should know that they have a problem with one of their valets.)
If you are using one of these new "on-demand" valet services, then they will probably be driving your car a greater distance, since it appears they lease spaces at less popular, more out-of-the-way garages and lots. (The further they drive, the greater the chance of damage.)
I feel that people with manual transmission vehicles are crazy to turn them over to valets. Because... most of them can't drive stick. They learn on-the-job. I sure do know what a burnt clutch smells like, because I've smelled it plenty of times.
There were plenty of times other valets ran to find me because they suddenly got handed the keys to a stick shift car and knew they couldn't drive it.
It is DIFFICULT to hire valets who have this skill.
Checkout what I wrote about this subject in more detail HERE.
Why was the key left unattended in the car? This is a management failure. I have the impression that sloppy key handling is a widespread issue at MANY valet operations. They simply make it too easy for criminals to hop in and drive away.
Just to remind you how important it is to leave nothing of value inside your car, here are a few more valet theft tweets.
We have the guy up top who had his jacket stolen, the Westin customer tipped his valet and then discovered that more than $2000 worth of camera equipment was stolen, and poor Gaby who was the victim of iPod theft. Nice, huh?
It's starting to look like a lot of valets are scum, wouldn't you say? And there's tons more tweets like this out there. Tip of the iceberg here!