I asked a question "how to do X (and is it possible to do X)".
I got an answer that's basically "I don't know how to do X" (The other text is not very relevant to my particular question, but might be of interest to others). To me, it seems that the answer would be much better, if the person who wrote it, stated whether he was an expert (which would imply "X is probably very hard, if not impossible").
However, when I suggested this, this person seemed to be offended, as if I'm asking him to "defend his credentials" (I don't know him at all, so I'm not aware of any credentials to defend).
Any suggestions on how to handle this? Not just in this case, but in the future? Was I being rude?