How would a startup that intends to provide a brand new type of service quantify the market potential without spending a lot of money on legitimate survey research? Or without rolling out the product on a small scale in a test market and then making assumptions about the larger market?
Take Groupon and Airbnb as examples. No similar services existed prior to these guys, so how could they (or how did they) estimate the number of potential consumers (or transactions, etc.) in these brand new markets? As far as I know, neither company targets a real specific demo, though both services might be more appealing for lower-income, budget-conscious consumers. But that's far too broad. How could you estimate the number of people who would be willing to sleep on a stranger's couch, given that this was never a real option before? And how would the numbers change if a new site were to facilitate matching and provide some legitimacy and security?
Follow-up question: Assuming that estimating the market size with even the slightest hint of accuracy is a virtually impossible task for a bootstrapping startup, can you get around this dilemma when seeking funding? What do you do when an investor asks about the potential market size and share?