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][1] to be quite helpful:

![illustration][2]

[1]: https://meta.stackexchange.com/q/225370/203389
[2]: https://i.sstatic.net/vAUaw.png