Building relationships with clients, same as it ever was. There are companies today that have been selling for example very specific machined parts for 100 years. You have never heard of them. They don’t advertise on facebook. Yet they bring in enough work to stay in business without these paid campaigns. The secret sauce? The rolodex and actually calling potential clients directly.
This answer is a good answer for some companies, but for other companies it's very hand-wavy. Paid ads have value and you can make a pretty penny even on Meta (actually, especially on Meta compared to others) if you do it right.
Still curious about alternatives for paid ads
What?
How do you meet these clients in the first place?
How do you get them to answer their phone?
How do you get word-of-mouth if you’re just starting out?
Edit: reduced level of snark
Well, about that thing. Some of our local companies in machining and other things somehow buy private emails and phone numbers. While I work at a place that do not directly need such services, my spam box and my work phone(mobile) blocklist is full of services calling me to offer their latest price and if I can forward them to my boss or whatever. So, either online ads or other forms of spamming.