I've been analyzing successful founder interviews for over 2 years now [1] and noticed for 'passive income' projects, usually they either:
a) Stay on top of Google for a few keywords
b) For mobile apps, they get a good ranking on AppStores
c) Are mentioned in some high-authority website as a resource, and that high-authority page ranks for some main keywords on Google
Word of mouth is rarely mentioned and that confirms various research studies [2] that the WOM effect is negligible if you're small.
[1] https://www.firstpayingusers.com
[2] https://business.linkedin.com/marketing-solutions/b2b-instit...