I wrote a program for a client on these forums recently... but did not get paid. It was very simple and short program that I was charging a very small fee to write so I wasn't bothered when they had asked for the program "to make sure it worked" before sending funds to my PayPal. I suppose that was a very naive thing to do. We exchanged quite a few private messages in short amount of time so it had struck me odd that he take so long to reply to my last message -- the message where I gave him the program. By this point, it is nearing 48 hours since our last message (I've sent him multiple) and I'm beginning to think that I've been swindled.
It's a mistake that a lot of people tend to make. The best you can do is count your losses, move on, and try to educate others on how many arseholes are out there.
Regarding similar stories, my sister recently started a small business creating poseable fantasy creatures where an individual didn't pay after the item was shipped (it wasn't a small fee either).
Fortunately most people don't make this mistake twice.
Don't sell to regular people, sell to companies. Companies do pay and if your app solves a problem for them (= it brings them real money), they pay well.
The times when you could earn good money from selling shareware, especially desktop apps, are long over. Actually it is very hard to earn good money on mobile apps too, even if you get your app into AppStore / GooglePlay.