There's actually a really simple solution to this. Always be aware of the condition of your car when you have it Valeted. Give the Valet 25-50% of what you plan to give him total when you hand him your keys. Be polite, honest and kind with the guy. Tell him "I like my car a great deal." Don't tell him "I think you're gonna **** up my car." Go inside, enjoy your meal. When you come back out, quickly go around the car looking for anything obvious, if there's an issue, stop right there and point it out. If there's not, take your keys and give him the rest of his tip. This is how, when I had my Grandmother's Lexus valeted, that I always made sure everything was perfect. Valets are just as important as waiters, if you piss them off enough, they WILL **** up your stuff on purpose, and if you insist on self-parking, then have the guy ride with you so you park where he wants you to, and tip him anyways so when he parks the car next to you he doesn't door the crap out of you.