I have been playing the game Valet Hero for 6 months, but have (as of yet) failed to get any of the secret achievements.
What are the secret achievements in Valet Hero?
I don't have all of them yet, so I'm going to have to come back and edit this answer to include other ones, but here are the ones I have so far:
Six down, seven to go.
These are pretty self-explanatory, although I think Super Sized is glitched. I got it (as well as the normal achievements Value Meal and Drive Thru) on silver challenges.