Why your first offer should be embarrassingly specific
Most new founders try to appeal to everyone, and end up appealing to no one. A broad offer like "marketing for small businesses" forces you to compete on price against thousands of others. A specific offer like "booked consultations for independent physical therapy clinics" instantly tells the right buyer that you understand their world.
Specificity also makes everything else easier. You know where your customers gather, what words they use and which problems keep them up at night. Your content writes itself, your outreach gets replies and your referrals multiply because clients know exactly who to send your way.
You can always expand later. Start narrow, win in one corner of the market and let success earn you the right to grow.