While the dream of most Indiehackers is to create a product with recurring revenue, services are often the easiest way to get the ball rolling. Also, there are many IHers who are operating full-time service-based businesses. But selling these services can be a tough job and you can't always rely on inbound/referrals.
Cold emails, done right, can definitely help.
I've been compiling cold email templates for a new project and came across some interesting ones. The examples are specific to services and can be used to start conversations from scratch.
Hope this is useful!