Post a job listing on your local Craigslist for the closest category to what you want to work on. Something like:

"Local educational startup looking for K-12 school teachers to survey"

I've done it multiple times for startup ideas and user testing. I've always got numerous replies. Most people are more than happy to have an email dialogue and many are also open to meeting in person to test your app.

If I take up more than 30 mins of their time, I usually get them a $5 Starbucks gift card or buy them lunch (I don't tell them ahead of time).

If you don't have the network, you have to build it. There's no real way around that. If you want to start a business and need to stress test your idea like this, you'll need to do outreach. Whether that's cold outreach or attending events or joining the right groups and communities, it's all about the legwork.

But the point is you can still do that on your own time without making huge sacrifices. Taking the concept of "go out and talk to people" too literally just serves to prevent you from actually finding and reaching your ideal audience.

Need to know where to start? Angel List, LinkedIn, Meetup, and the like. Write some cold emails. You can always build a network, and you should if you want to start a business.

So I have this problem, I built an mvp and signup page, attracted a lot of page views, got quite a few signups for the free tier (50 for example) and they were all of the type: sign up, login, look around, never came back. So using these 50 signups/emails as my network, I've done two things; emailed a survey link, and emailed just asking for feedback. And nothing, not one single response to either the survey, or the email. Of the 50 only one unsubscribed.

What am I to make of this? Is the fact I got 50 signups a signal the product has value and I should continue, or does the fact users don't return a signal the product is crap I should scrap it? I'm really at a loss here.

Aside from trying harder to reach those people, you possibly don't have a large enough sample. It is also possible you attracted the wrong people. For example, I'm in a space where there are lots of competing free products and we are a paid one. Just as one example, I had to put "free" as a broad negative keyword in AdWords to try to filter them out. Turns out there are entire classes of keywords that tends to resonate more with people looking for a free solution vs paid that I had to uncover and filter for.

I would suggest trying harder to get in touch with those free signups. Write them personal mails, not newsletter/ survey sounding mass mail. Pick 10 of them, tell them you are the founder, tell them why you started it and need there help finetuning the product, that you don't want to sell them anything but offer them $20 for a short Skype etc.

start with what you want to measure - what exactly is the metric for success here? is it just signups?

might help us to know a bit about what the product is, but is there something specific that users should be doing in this free tier? what % of the 50 are taking this action?

Best way i found to find people to evaluate my business ideas was putting up cheap ads on internet. Started with Adwords five years ago.

Then you drive them to an landing page where you ask for the sale. But right before the purchase, you specify that the product is under development and will be shipped at an specific date. Thanks your "almost costumer" and collect his email for a future launch.

I think the internet is your best tool here, specially if you have some bucks to spend.

For your used car sales niche example, I'd recommend to look at used cars dealerships.

That is not really the hard part. It is a great excuse, and I use it myself to convince me I shouldn't look. But it's not really the hard part.

Usertesting, invision prototype, also: local people on the street