If you're not 100% certain a valet is a real valet, snap a photo of their face before you hand over the key.
This does happen. When you are about to valet park your car, size up the valet.
Are they wearing a uniform that looks like a valet uniform? Do they have a name tag? Is there anything on the uniform that identifies the valet company? Are there other valets nearby wearing the same uniform?
It doesn't hurt to ask questions:
"Hi. I'm thinking of valet parking my car..."
How much does valet parking cost here?
Will you give me a claim ticket?
Do I pay now or when I get my car back?
Is there a way to call ahead so that I don't have to wait?
What number would that be?
How late are you open till today?
Are you the one who will be parking my car?
Where will you be parking it?
How long have you been working as a valet here?
What happens if you guys are closed when I come back to get my car?
What's the name of your valet company?
"Sorry, I'm new to valet parking. That's why I have to ask so many questions."
Snap a photo or videotape the few coins you left in the cup-holder, snap a shot of the odometer reading, turn the car off, keep the key in your hand while snapping a shot of the valet's face.
If you have a phony valet in front of you, they probably will be running down the street at this point.
Backing up a bit, if you have a funny feeling about this valet at any point in your questioning, like if the valet has an unkempt appearance, or if your intuition is telling you something isn't right, there's no need to be polite. Just drive away and park someplace else. Better safe than sorry.
But if you are now standing outside your car and suddenly your intuition is raising concern, then ask the valet to get their manager. And as they get further away from the car, you should get back in your car. Start up the engine. If they are coming back and there is nobody with them that looks like a manager, then just put it in gear and go.
And if a manager shows up, you can just say you wanted to be certain you were dealing with a real valet worker.
At this point, begin snapping photos of all sides and corners of your car to document the condition of your car at the exact moment you turned it over to them. You will need this time-stamped evidence to pressure them to compensate you if they somehow damage the car.
I recommend tipping your valet at arrival to influence the quality of care your car receives.
When you get the car back, do an immediate and complete vehicle damage audit before you drive away. This is critical. If you find the damage later, they will say it's not their problem.
Check for damage. See if your spare coins in the cup-holder are still there. Use your phone to record you going straight to that cup-holder. Check the odometer reading.
If nothing is missing. If there is no new damage. If the odometer has barely moved, then as a courtesy I recommend tipping the valet staff again.
Five bucks on arrival is usually good. Two bucks on departure is the minimum. No coins. And never just a dollar.
Now if you discover that the coins in your cup-holder are missing, have the valet manager summoned.
You are going to reveal that a thief is in their midst. You will demand that your lost change be replaced, as well as demand a return of the parking fee you paid.
The only defense they have is that they might have left the car unlocked or left a window down. If that's the case, then this is sloppy work and the loss is their fault. Demand full reimbursement.
(Leave two or three quarters in there at the most, not a load of change.)
By the way, a lot of valets will steal that change. But since you tipped up-front, they should have certainly left that change alone.