May, this is a fantastic post! I understand how you feel.
Allow me to say something that might ease things and make it easier to sell your ideas like a million-dollar service.
From my personal experience being in business for a long time, most of your clients will not have 20% of the knowledge that you have; they don't know what you know.
What might look average to you will look excellent to them.
Even if you believe that you can't deliver top-notch work, sell it with confidence anyway and later figure out how to make it unforgettable.
You are not only highly talented but also have a high standard which is rarely found. Your clients will appreciate that.
To them, It's not a matter of writing an article; instead is a matter of working with the right person that they trust.
The worst thing that could happen is to refund the money and apologize or hire a freelancer to take over the work.
You can always find a way to make things work out, but first, you need to grab the opportunity.
After all, money loves confidence and speed.
Thank you for the mention. I hope this helps a little. And btw you have a great style of writing.