See, here’s an example I noticed today:
During the week, I daven in a shul that davens nusach Sefard. There is a fellow who sits in front of me who (as I do) davens nusach Ashkenaz. When the chazzan finishes Chazaras HaShatz, he sits down to say Tachanun and he is seated and saying Tachanun when the Tzibbur is reciting the thirteen Middos.
I’m pretty sure (but not absolutely sure — see later) that the thirteen Middos are similar to Barchu, Kedusha, etc. where, even if it’s not your nusach, if the tzibbur is saying it, you should say it with them. So, even if he’s not going to recite vidduy, he *should* at least be standing when the tzibbur recites the Middos and say it with them.
However, I will not correct him. First of all, as I said, I believe that I’m correct, but I’m not certain of it. I’m not going to correct someone for something where I, myself, am not certain of the answer.
Second, I don’t know the person. It’s one thing if I were to go over to a friend who knows I have his best interests at heart and where I know s/he will take it in the spirit intended. Here, however, I don’t know this person. While I wouldn’t mind a perfect stranger coming up to me and (in a nice and civil tone) informing me of a mistake I’m making, I know that not everyone is similarly disposed to random criticism from strangers.
Third, I have neither the spiritual courage nor the fortitude to approach a stranger regarding corrections. Yeah, I know some of you will say that’s a cop-out, but, nonetheless, that’s the reality.
The Wolf