Extraordinary ability to track down issues on virtually any make of car. Mine is 20 years old, so has aging problems that are normal for older cars: i.e., brakes, oil hoses, alternators, A/C, squeaks, etc. If it can be fixed, there's a 95% chance Mr. Gray can do it, at a reasonable cost.
Here's my suggestion: Since Mr. Gray is the only trained mechanic and needs to get each customer in and out promptly, it might be of value if he could have an extra pair of eyes to briefly inspect the exterior of each car before the customer drives away.
For example: Two separate occasions an extra "pair of eyes" would have caught these oversights: First time the battery was too weak to start, so he had to jump start it, eventually replaced the battery and the alternator. Second time there was piece of Trim on the lower fender noticeably protruding (mishap during service obviously) and he removed a screw, realigned the Trim, and reset the screw. His helper might have seen that had he been given the task to just walk around the car and "eyeball" it. The nearly dead battery also could have been detected if a helper would have started it to leave in front for pick up.
These things happen and are corrected in time with a positive attitude. None the less, he's one of the best!
"Extra pair of eyes".