Example: this one. We know now this is a fake.
Is there a consensus on what to do with it?
Suggest the OP to ask for the reasons that this cannot be real.
Seems a good choice to me, as the explanation can be reused for other fakes, and is overall interesting and educational.
This may lead to more questions of this kind in the future, which may or may not be what we want.
Suggest the owner of the comment saying it's a fake to write an answer.
A bit like the previous option, but the answer doesn't answer the actual question, the title will be misleading vs. the content.
The comment will be visible. However this question may be closed/deleted sooner or later.
Vote to close and/or delete it.
The premises of the question are wrong, hence there is no correct answer.