Downvote, comment, upvote good answers, make a better answer if you can, move on.
You could also add a bounty to try to encourage better answers, if you want.
Wrong vs. "demonstrably wrong" is not a distinction we make here. Technically incorrect answers should be voted down--that (and optionally commenting) is all the action that needs to be taken. Unless ...
Ideally, the way it ought to work is to write a better answer.
In practice, it will be difficult to displace the wrong answer. It already has upvotes, and was awarded a bounty. You might be able to get the question asker to accept your answer, if that user is still active.
The hard part is to attract users to your new answer to an old question, so it ...
You wanted a more specific answer than what Rory gave you, so here is my best shot.
Sometimes we treat experience and prior history of good answers as a proxy for verification (like with Mark Adler, as you mentioned in the comments). This is not because these are good measures of verification in and of themselves, but because we recognize that there are ...
If one or more answers helped you, and you want to accept one, you should accept the answer that most helped you.
Whilst knowing the background or qualifications of an answerer could help you with assurance over accuracy, the vast majority of accepts have nothing to do with that.
Remember if a better answer comes later you can even change your acceptance.