nearly 30 years ago, I worked as a valet for a posh Connecticut Country Club - an interesting summer job. Most valets are honest and hard-working...but, treat them poorly, stiff them a few times, or treat them like they're your servant, and you've set the tone on how you would like your car to be treated.
The sweet little old lady, in her canary yellow caddie with less than 8,000 miles on it, always, and I mean always, gave me a quarter...but to her, that was a big deal, she was a child of the depression...so her caddie was always treated carefully.
The owner of the local Rolls-Royce dealership always gave me $5 up front, along with some instructions on parking his Corniche Convertible...and I followed them to the letter.
The jerk with the black Jag, who always "forgot" to have change, who ordered me around like an indentured servant? Well...when the lot was full, I had to chose which cars to park near the 18th green...
Not excusing this behaviour (reminds me of the two guys in Ferris Bueller's Day Off), but if you take care of the valet (in advance if you're new to the place), and treat him with some decency, he'll take care of your car.
You should see how carefully the valets treat my 1990 4Runner (hardly an expensive car) when I chat with them like equals and give them a few $$ in advance....