Before launching an app in Apple's iPhone App Store, it would be useful to have at least a vague idea of the sales potential. But how on earth am I going to estimate this?
As an example, let's take a small productivity app with a certain detail that makes it unique and desirable, at least to your niche market that is productivity-oriented iDevice owners. You could sell this app for the obligatory $1. For such a product, you would have a pretty clear idea of how to sell it; elevator pitch, typical user profile, etc. But we have no idea about the customer demographics in the App Store.
This could sell 20 copies in a year, or 20 000, or even 20 million -- who knows? Given that there are more than 300 million iDevices around and 35 million activated last quarter, the market potential is staggering. Even getting literally one customer in a million would bring income.
How can I get an idea of what to expect, in terms of copies sold?