One line answers themselves aren't necessarily bad. "To fix this foo the bar" is an answer. Not the most descriptive answer, but is one. Don't flag these. I don't downvote these, but you are free to if you really feel you should. I don't see any reason why.
When an answer is nothing but a link and some text, e.g. "yo, check out my blog for the solution [link]" then it should be flagged as "not an answer". A quick any easy way to test this is to imagine the answer without the link. Does it still try to answer the question? For example:
You need to foo the bar, see my blog [link]
This is an answer. If you remove the link most of the answer is still there. This meanwhile:
to fix this see my blog [link]
is not an answer. If we remove the link no useful information remains.
I find Shog9's illustration of this to be quite helpful: