You're absolutely right. If the answer's sole purpose is to request further details, then it should have been a comment.
Examples:
Please foo that bar and then post the results.
Can you try yaking that baz in your preferences? Does that work?
As @Paul mentioned, simply flag those posts as not an answer. We'll check, delete the posts, or migrate them to a comment instead. No big deal. That being said, if there's a repeated pattern of a user posting half-baked answers that don't provide a solution (instead of commenting), we'll probably let them know through other means that this is not acceptable.
Read more about that: When is an answer eligible to be flagged as “not an answer”? What to do?
Of course, if the answer actually explains what to do with these results, then that's a different story. As you correctly observed, our posts should be useful to visitors with the same issue, so there might be no possibility to interact with either the OP or the person answering the question.
So, something like that would be okay:
Please foo that bar and then post the results. If you see this and that, this means you need to change these settings there and restart. If on the other hand they show that blah blah, the error is caused by magic unicorns et cetera.