If he wanted something different because his arm was bothering him with RPM at 58 (which is too high for poly anyway), then you should have given him RPM at 44lbs. I had a client who insisted I string is RPM at 58 and not lower. When he came back to get restrung we consulted again and he indicated he was having some arm soreness after playing sometimes. Told him to just humor me one time and let me string it at a different tension. I strung it and gave it back to him without telling him what it was. Just told him to go play and see what happens. He came back happy and I told him it was 44lbs. He was shocked that 44 wasn't causing him to hit everything out. He actually played better with the lower tension and no more arm pain.
I never suggest normal players to play with poly anywhere in the 50's. Always 40's (mid to low). Nobody believe it until they try it. It's like everyone's been sold on the idea that if it's not strung at 60, you'll hit out.