I was just at a car wash today. I got the premium wash, which was normally $13.99 but I had a coupon for $9.99. The guy who finishes the car--by this I mean does the drying, windows and tires, no hand wax--took about 10 minutes for the job, diligently working the whole time. I tipped him $3 but I have no idea if this is appropriate. Does this sound right? What would you guys tip?