I did not market or sell this service. Back when I did this free, I worked closely with my mentor who had a startup (which later was acquired by a publicly listed company). I helped his company a lot. They were building an BI platform for big data.

That success gave me wings for a while. Word of mouth referring helped and I only took on clients who were recommended to me (i.e. they were aware of it)

Sometimes I meet business owners and founders at meetups or for lunch and we organically start talking about what we do (with no intention to sell). I always try to make the other person curious and then feed their curiosity. Also, I do an initial consultation for free.

The motivation is not money and my rates are pretty compelling (low) for the ROI I promise. Not every small business takes the opportunity but some did.