If it's anything like how Japanese-esq culture is presented in L5R? They will be offended that you shamed them by exposing it. They are, however, shamed. And if you do it as artfully as your letter, VV, suggests, they're shamed so hard that you might be spared actual shame, yourself, for exposing it.
It's kind-of related to Kibun; if you're so offended by the lie, so hurt by it, that it is impossible to ignore it and politely hide the spectacle, then it's their fault for being so discourteous and insincere. The sticky point is if they sounded believable enough that you calling them out is rude rather than inevitable.