We sometimes reflexively respond with “No problem” when a client or customer says “thank you” for a superior service. Jim Blasinggame, one of the world foremost experts on Small Business and Entreprenuership wrote an article that say this IS a problem. We should say “You are most welcome!” instead of “No problem”. (Or you can hit them with a referal request?)
The semantics involve might actually get people receiving the “No problem” reply to think that what they did caused a problem in the first place! Read more about the article here.