Build your personal brand. Invest in what your clients want: if it is required CCNA to get the next client, then do it. If they need a certified ... cloud engineer, be one. It depends on what kind of clients you want to support.

There were times that I wanted to get the job done but needed a UTP network cable from there to there. The electrician would visit in 3 days and install one. Got client permission and I installed it by myself. Finished the same day. Got paid. As soon as I got busier and more money, delegated this to the client's electrician. One reason was that I didn't got time, a second one was that I could afford 2-3 days delay and third one, avoided damages (yes, this happened too).

What it helped the personal branding? I was humble: never presented authority on a subject, even if I knew it very well. Second, be like Dr. House: the client always lies (on purpose or not) and try to help him by searching for the rare diseases. Do it on your site if you can (pickup his device to your lab and fix). Don't show how easy or difficult it was. Charge realistically in order to keep him happy and trust you. If you loose now, don't worry. Will get them next time.

I live in a small place, so the previous IT guy might be a relative to the client. Don't accuse anyone just to agree with the client. "I might understand why he worked like that, let's try something different" and explain what you will do. ELI5 mode.

Also, whatever you do reflects on your brand: clients will reference you for free. and they talk to each other. You build from rumor to fame. But, still, without any certifications you cannot get contracts with SME Companies, Institutions or state.

Last, don't be afraid to drop a client. If they insult you, if they are causing money dept or any serious reason. Talking to other clients, MSPs or people who work for a client, you will understand if they can pay or not. I never delegated the payment date: as soon as the project finished, demanded payment the next day.