This particular story took place at the range, not a gun shop. And it is a mix of stupidity of both word and action. It is also an abject lesson in the importance of observation and why you should never assume. But one afternoon, we had a guy show up at the range to zero a new rifle that he had bought and put together. He had put a Nikon (maybe a Prostaff) type scope on it. He could not get it to zero, and said it was wandering all over the place. One of the regulars was at the bench to his left and had been casually spotting they guy's shots with his own rifle's scope, and trying to give him corrections. But no matter how hard he tried, the guy's shots kept wandering all over the target.
I happened to be walking by, and hearing about his troubles, I grabbed a spotting scope and also tried to help. My gut instinct was that the guy was probably just a typical noob that thought that once dialed in, the rifle would automatically always hit where the crosshairs were, without regard to his own shooting fundamentals and technique (or lack thereof). I've seen a lot of new folks trying to zero a scope by shooting one shot, then dialing to that hole; then shooting another shot, and dialing to THAT hole - and end up just chasing bullets around all over the target. I figured this was gonna be the problem. So I had him take a shot at a spot on the target and he was about 4 MOA left. Then I told him to make a windage correction of about 4 MOA right, and his shot was the same windage as his first shot, but his impact had moved close to 4 MOA high. I figured he jerked it, so I told him to make sure he was steady and send another one. He did, and it was right beside the previous shot, about 4 MOA high. So, I told him to dial an elevation correction 4 MOA down. He made the adjustment and sent another round. The impact was at the same elevation as the last 2 shots, but about 4 MOA right. I told him to send another and it was right beside the previous shot - 4 MOA right. He was bitching about the scope being a piece of crap, etc. So I told him to dial the windage 4 MOA left and see where it went. I decided to watch him dial it, because I really didn't know what he was doing. He then reaches up and starts turning the top (elevation turret). I tell him to stop, that he is turning the elevation turret, and he says "no, this is the windage turret". I tell him "no, that is the elevation turret". He then points to the dial on it and says "no, it says left and right on it". At this point, I actually take a good look at the scope and it hits me like a ton of bricks. Dude has installed the scope 90 degrees sideways, with the elevation turret to the left, and the windage turret on the top. I had not even noticed it to this point. I told him that he had the scope mounted wrong and that the elevation turret was supposed to be up and the windage knob to the right. He then said very condescendingly to me, "No, THIS is better, because I am left-handed."
I just had to walk away. Where to even begin...