What does "Service-based startup" mean? As I was taught to think about it, Reddit is technically a service. My company, Matasano, is a services firm (we consult on software security) and we sell a product. Plenty of companies in my space offer coin-op professional services; log in, push a button, and something will do a network security test for you.
Which kind of "service" do you mean?
I'd meant client based, $P/H work. Design, development, consultancy etc.
Even I wouldn't call companies like that a "startup". There's a VC-backed shoot-the-moon vanity startup bias on HN, for sure, and it manifests itself in arguments about what the word "startup" means --- but nobody I know calls consultancies startups.
You should hit searchyc.com and look up submissions containing the word "Freelance"; they tend to have the best info about consulting.
I'd say choose your clients wisely - avoid timewasters, and clients which aren't likely to scale.
Focus on making a really great product. Everything else will follow.