When someone posts a question, which asks for verification of their proof of something, the mathematical content of that question will often be a duplicate of another question.
Now, in order to help the asker, the question should not be closed as a duplicate, since it is highly unlikely that the actual question is a duplicate (this would require someone else to have asked for verification of a proof that was identical to the one given by the asker).
On the other hand, once the verification of the proof has been dealt with, it seems like it might be a good idea to mark the question as a duplicate (assuming the mathematical content really is a duplicate of course), since a later visitor searching for phrases related to the question might come across this one first, and it would likely help them to be redirected to a place where the question was about the mathematical content, rather than on the details of a specific attempt at a proof.
I would therefore propose that when people see a question where the verification of the proof has been dealt with, they vote to close as a duplicate.
(This proposal is inspired by the question Any two sets $Y$, $Z$ have the same cardinality $\iff$ there are injective functions $f: Y \rightarrow Z$ and $g: Z \rightarrow Y$. and the request for reopening of it).
As I may well be overlooking something important here, this thread is of course also an invitation to discuss the proposal.