> I get customers can be hard but "can't replicate it" translates directly into "find another service provider".

Omitted for brevity (as others have pointed out in the comments): we maintained a relationship with the customer long after the exchange. The goal definitely wasn't to get him to "find another service provider" so much as it was to reset the tone.

All that being said, clearly my casual response ("can't replicate it") definitely was the wrong thing to do, as I didn't intend it to offend at all.