I don't know why are all scared from black hat SEO? Do you you think White hat is white? It is actually many shades of grey instead.

Rarely a guest post is accepted for free, usually a payment is required a post to be published on another site.

Running a PPC ad campaign requires to pay. Isn't it a black hat too?

There are many hats in the SEO world and I've tried to list them in my android app here: https://play.google.com/store/apps/details?id=io.kodular.colen.seohats&hl=en&gl=US