E-commerce Link: Research 101
While it doesn't generally work well for usability evaluation or hour-long one-on-one interviews, grabbing folks in a particular situation can prove to be a very valuable, not to mention inexpensive, discovery research technique. This method works best when you would like to speak with recruits in context or in the moment.
We've had luck with this for a major fast food chain when redesigning its public-facing website. We offered a $10 coupon for 15 minutes of people's time as they came in or out of the restaurant. We also have used this technique with customers waiting to have their cars serviced or batteries replaced at an auto service center. Our findings fueled the strategy for a battery site redesign. We've even chatted up those waiting for flights and connections in busy Chicago airports, all in service of the design of desktop as well as mobile airport website experiences. Captive audiences can relay really personal and pointed thoughts to a discovery researcher.
Do Your Homework
With all three approaches, we want to stress that less expensive recruiting methods absolutely do not mean less legwork or due diligence. Even guerilla recruits should be purposefully chosen, and, no matter what the circumstance, researchers should draft formal screeners to make sure they're getting the right mix of appropriate participants. The pool of recruits must meet agreed-upon qualifications and not just be warm bodies filling research slots. Be choosey.
In hindsight, we should have confirmed right from the beginning that customer lists would be absolutely available for our specialized industrial gas research. If we had learned early in our work that client-supplied lists weren't a possibility, we would have suggested splurging on recruiting through a market research firm. This would have ensured that our participants were qualified and capable of offering truly relevant opinions. It also would have saved us quite a scramble in trying to pull together discovery research activities.