If you have 30 clients and a monthly income of £5,000, their capacity to spend money with you goes like this:
Your best customer generates 20% of your business (£1,000).
The next two generate the next 20%.
The next 20% comes from the next four customers.
The next 20% comes from the next eight customers.
The 15 of your customers at the bottom generate just 20% of your business. You could fire them, save yourself a load of hassle, and concentrate on building great relationships with all the others. You've got £4,000pcm but only half the hassle. Fire half your clients and start taking Fridays off.
I once got 'fired' as a client by a mail distribution company. He didn't even do it subtly. It hurt, but he was right. I was small time.
The normal alternative might be to separate out that final 20% and give it to someone to handle. Who knows, they might shine. So long as the problems don't escalate, the reviews aren't bad, the reputational damage is zilch.
So, easy life, fire half your clients. And determine what sort of clients you won't deal with any more.