A brief concept that seems nonetheless worthy of consideration:
If you polled a number of people on whether they would buy your product, on a likeliness scale of 1-10, who do you consider a potential customer?
If you're an optimist, you might say anybody over a five is more likely than not to buy. But this obscures what your test is really about: how many perfect customers exist for this product?
Continuing the concept of Product-Market Fit, the perfect customers are those consumers that your product addresses the needs of with pinpoint accuracy. These customers would be willing to put in extra work to acquire your product, and that's important, because it's highly possible that in your early days you aren't going to get everything right, and you'll put your customers in a position of having to do a little extra work to buy from you. Those who do constitute the audience you've achieved an excellent fit with.
It's vitally important that you hold onto these customers, because besides potentially becoming investors, they'll provide you with excellent feedback, valuable referrals, and an important barometer of your success. To think about some of the ways you should strive to keep them engaged, read on.