I did this building a small agency in the marketing and ad space.

Happy to advise on specifics but in general here’s how we did it:

Build up a portfolio of content (since we develop content) that shows we know what we’re doing.

Go on speaking circuit for your niche and give lectures on your expertise.

Take whatever comes your way for first few deals. Always get a solid statement of work & contract.

Rinse and repeat. If you’re ok with going slower this works well. I manage a team of 9 now and after some serious time spent training them I mostly just approve work and put out fires with clients.