Black hat vs White hat is very poorly defined. Everybody has different definitions of what is in each. Google views any attempt to manipulate the rankings as black hat. I think any practice you would have a hard time explaining to Google would fall in that bucket. Unfortunately that pretty much means there is no White Hat SEO because those footer links, the blog you have on the side, the cross linking with your friends website, Those exact match anchors you put on the page, and that keyword density you increased to reach competitive parity with page one are ALL efforts to manipulate the rankings.

I think it is better to view it all in terms of SEO that works vs SEO that doesn't and risk mitigation. I often explain to clients that how Google reacts in the future is out of my control but Target, Walmart, Amazon, ... all engage in the thing I am recommending (cite examples) and that the risks are ...

Let the client choose each and every time. Its their business... Let them make the call. If you try to live a pure White Hat life as an SEO then you are probably living a lie.

Just my opinion.

Unrelated Keywords
Keyword Stuffing
Tiny Text, Hidden Text, and Hidden Links
Cloaking
Doorway Pages
Page Swapping
Duplicate Content or Mirror Site
Spam Blogs