In this answer https://blender.stackexchange.com/a/39779/1853 the poster copied and pasted from blender guru's website. No attribution is given or even a link as if he/she had written the text. What is the policy for this case?
(This link pretty much says it all.) *I did not see your comment when I wrote this*
What to do when plagiarism is discovered
If it is something small, say part of a description of some node copied from the manual, then just edit the post and add in the proper attribution and blockquotes.
However it is is an entire post, like the linked example, or the user has a history of this type of thing then just flag it.
When you flag for a moderator's attention please use a custom flag message something like:
This post looks like plagiarism, < url to original source >
When you add the original url so the mods can check and see that this was in fact plagiarism, it will exponentially boost your chances of getting a helpful flag.