The guy at the camera shop in Denver told me to stop cleaning my lens every time, and he was right
I used to wipe down my old Pentax lens after every single roll, thought I was being careful. Then last month the guy behind the counter at a shop on Broadway asked what I was using and said "you're grinding grit right into the coating, quit it." He showed me a tiny scratch under his loupe that he said came from dry cloth wiping, not real use. So now I only brush off dust and use a damp cloth maybe every 6 rolls, and my shots look the same or better. Anyone else get talked out of over-cleaning their gear by a shop guy?
Did the shop guy actually show you the scratch through the loupe, or just tell you about it? Either way, I feel for you, because that dry cloth habit is so easy to fall into when you think you're doing the right thing. I did the same with an old 50mm for years and probably put a few fine marks on the coating without ever knowing. It's a bummer to find out later that being careful was actually the problem. Good on you for listening to him though, most of us just nod and keep wiping.