Sometimes you just happen to read an answer in a topic in which you are not an expert in, and it sounds convincing enough, it shows careful effort and attention to details in the writing, and the author seems knowledgeable enough about the subject (see notes below), but this is simply not your area of expertise and you can't honestly say if it's correct or not.
What do you do? Do you upvote?
Note: there's a distantly related phenomenon of upvoting because of author's high rep (e.g. Upvoting based on celebrity, too many upvotes (“excessive rep slurping”) and The Problem with Reputation: Does High Reputation Attract Too Many ‘Up-Votes’?). This scenario is different in that while a person's rep may play a factor, it's only a supporting one.
Ultimately the perceived high quality of the answer itself is why you think it may deserve an upvote, and the problem of whether or not it's responsible for you to do it is there even if the person has a low rep.
To complicate matters, and to anticipate the arguments that votes are based on usefulness not correctness, let's say that the answer is pretty much useless for you. Perhaps it's related to an obscure language that you don't plan on picking up any time soon, or perhaps it's an area not in your career direction at the moment, etc.
...and yet you somehow saw this question/answer. Hey, these things happen.
So the answer is useless, and you don't know if it's correct or not, and yet somehow (based on subjective factors, perhaps) you think maybe it deserves an upvote. Is it responsible to do so?