Just so that this question has an answer:
One method is to post your own answer to the question. In passing, it can demonstrate that an alternative strategy is not correct.
If the answer to the question is not known, then asking and answering a question can be one method to provide a demonstration.
As always is the case with interacting with other users, ...
I would probably go for one of these:
Ask clarifying questions.
These should ideally lead to edits to the answer instead of comment replies.
If the poster made unsupported claims or had a few missing (and impossible) steps in their argument, you can ask them to expand on that.
This could give you a much smaller part to disagree with, in that you don't need ...