A quick, good example of a very focused first target micro-segment is Honestly.com
“Previously, access to Unvarnished has been limited to invite-only or professionals from a list of roughly 200 pre-approved tech/tech-related companies.” From Techcrunch.
By intentionally limiting their initial base, not just through a private beta, but by actually specifically only allowing a certain segment of people in, they get a stronger response.
For them it’s obvious why this is the case. If I’m going to be able and motivated to give feedback on a colleague, chances are they work at the same company.
Facebook did this as well by only allowing Harvard Students, then college students, then highschool, then the world. If they did the world day one, they wouldn’t have made it.
Lesson: Forcefully limit your initial base to a focused, small group and you’ll get stronger results.