Originally Posted by robE
Any decent app will sell, especially the free ones with in-app purchases
Not really. There's usually dozens (at least) of any concept already in the app store, some of which will be free. So you're already releasing your product to compete with free apps. Then you have the issue that existing apps have more exposure (word of mouth, etc) and higher download figures which also pushes their ranking up. So you have to search more to find your app compared to popular established ones. Then there's the issue of advertising, games studios (etc) will throw a lot of money behind having their app appear in the Google's recommended slot - which most freelance devs just couldn't afford to do (and that's discounting TV / magazine ads which also happens).
It's very rare for a freelance developer to make any substantial return on mobile apps. And that's even without taking the development time / cost into account. So I really wouldn't recommend mobile app development as a career opportunity. It's an already massively saturated market which you'll have to compete with both the studios who can afford to promote their apps while being undercut by other freelance devs who give their stuff away for free. Thus you're far better off building apps as a hobby and hoping one of them goes viral than depending on it as your income.