The title looks like this question on meta How to deal with posters of consistent poor quality/incorrect answers but mine is more straightforward.
What to do with incorrect answers? Often they can be flagged as 'low quality' as rightfully commented in the linked question above. However, now and then it occurs that someone posts an incorrect answer but with acceptable quality content-wise (mostly not great, however, as it is incorrect :-). I mean, the facts are there, it just isn't applicable to the question. For example, I saw a question on peripheral adaptation and the answer from a first-time Biology user went about a somewhat distantly related process in the cortex. From a physiological standpoint an incorrect answer.
- Leave it alone and just comment; and/or
- Flag it for deletion; and/or
- Downvote? (somehow I don't like downvoting 'nice-tries').