Sam Shepler tells his story in a recent interview…

during my senior year of college… I didn’t have a ton of marketable skills, but one thing I did have was decent video production skills and a knack for marketing…

With a couple friends, I started a video production agency, Skyscope Creative, that peaked around $750k before we sold it

Later…

I needed to pay some bills and I asked myself, “What can I do that I know will at least generate some revenue relatively quickly” and “Can I take a part of what we did at our previous agency and productize it? …

I ended up “unbundling” one of the core most popular services of our agency — testimonial videos — and then set about productizing it.

That was the beginning of Testimonial Hero, which now earns $5M per year

And a nice framework there for starting your own productized service business…

Look at successful agencies and the services they offer.
Unbundle one of their core offerings and focus on that that.