Here's the meat of it, reposted from an HN comment since it is my most succinct account of the story:
A spiritually similar example: Appointment Reminder didn't actually exist in summer 2010, but I had a two-page demo of it set up. I got $400 out of an ATM when I went home to Chicago to visit, and just wandered around the Gold Coast/Magnificent Mile region of the city looking for every hair salon and massage therapy practice I could find. I asked them all if I they took walk-ins and, if so, could I have 30 minutes of the owner's time for whatever the rate was ($30 or so). In lieu of the shoulder massage/etc, I said "I'm interested in the massage therapy industry. Would you mind if we just chatted for half an hour about it?" And I asked about how they handled scheduling, appointments, no-shows, etc etc. I also did a demo of my two-page AR mini-app on the iPad and asked if they would be interested in buying it when it was ready.
I think only one person actually accepted my money for the interviews. I got five-ish "Please tell me when that is ready" out of a dozen or so conversations. No Bay Area or signup form required. (I put their emails in a paper notebook. And lost it prior to launch. Whoopsie.)
This was mostly successful for me: it confirmed that there was a market willing to pay for AR without me needing to actually build it to demonstrate that. (My sampling technique, which found only massage therapists/hair salons, did sort of lead me off the rails as to who I'd eventually end up targeting for most of the business. D'oh.)
A spiritually similar example: Appointment Reminder didn't actually exist in summer 2010, but I had a two-page demo of it set up. I got $400 out of an ATM when I went home to Chicago to visit, and just wandered around the Gold Coast/Magnificent Mile region of the city looking for every hair salon and massage therapy practice I could find. I asked them all if I they took walk-ins and, if so, could I have 30 minutes of the owner's time for whatever the rate was ($30 or so). In lieu of the shoulder massage/etc, I said "I'm interested in the massage therapy industry. Would you mind if we just chatted for half an hour about it?" And I asked about how they handled scheduling, appointments, no-shows, etc etc. I also did a demo of my two-page AR mini-app on the iPad and asked if they would be interested in buying it when it was ready. I think only one person actually accepted my money for the interviews. I got five-ish "Please tell me when that is ready" out of a dozen or so conversations. No Bay Area or signup form required. (I put their emails in a paper notebook. And lost it prior to launch. Whoopsie.) This was mostly successful for me: it confirmed that there was a market willing to pay for AR without me needing to actually build it to demonstrate that. (My sampling technique, which found only massage therapists/hair salons, did sort of lead me off the rails as to who I'd eventually end up targeting for most of the business. D'oh.)