Comment by photochemsyn

Some of the best products don't need advertising at all. Raspberry Pis for example, I actually cannot recall ever seeing an ad for a Raspberry Pi. Word of mouth, seeing examples of it in use - now you might call a Youtube video on how to set up a Pi as a headless server on your local network 'guerrilla marketing' or something, but I rather doubt that was paid for, people just like showing off their little Pi projects.