Black hat seo is an unethical technique which are applied by web users to get shortcut success. This is a technique which don't follow search engine's rules
Screw search engine rules.
I used to be a squeaky clean White Hatter and did everything by the SE rules book and along comes Penguin and Panda and a massively successful 15 year old site gets flushed down the toilet.
Do whatever it takes to make money NOW, the search engines do.
Just don't dip into the hacking area of Black Hat, as some things may be slightly shady and considered unethical, oh boo hoo, but other things the BHs are now doing are flat out illegal and should be avoided at all costs.
Truth is whether you do White or Black methods you run the risk of getting your site trashed these days so the only thing is don't whine if your site gets dumped if you're doing riskier things, it's gambling, and many are getting paid well doing it but they know the risks involved and have a PLAN B if they lose one site, there are always many more.
When you play the riskier game you need to step up the volume of the sites created and vary the methods and techniques used per site to avoid losing them all at once which can happen if you leave any easily identifiable fingerprints.
Multiple servers, multiple IPs, multiple templates ... minimize trackability so you don't lose your entire network of sites.
FYI, I'm not advocating BH but you need to almost act like a BH these days with varying servers, IPs and templates just to avoid the next Google update trashing ALL your sites.