For many professional service providers, easily 70% or more of their business comes from referrals. This is particularly true for lawyers. I know a number of people who never advertise and really don’t do any kind of active marketing.
They rely on word of mouth. A good word from a satisfied client is the best advertising there is.
That’s great, except for one thing. Your clients may be delighted with the service you’ve provided, but unless somebody asks them to recommend a provider in your field … or you get bold and ask them to introduce you to people they think you could help … they’re not talking about you.