But it shouldn't be. We, as developers, shouldn't harbor any ill will toward the OP should he decide to pull the open source version and sell it for profit. We certainly shouldn't advise him against it or recommend an alternative open source license that better guarantees that nobody can make money off this excellent piece of software.
Geeks like us tend to have a natural aversion to making money by selling our work directly, as though it's somehow dirty or wrong in some way that we can't quite articulate.
But we need to get over that.
We have a guy here (patio11) whose job this normally is, but he seems to have taken the morning off so I'll do this in his place:
On behalf of the Internet, I hereby grant you, the developer, permission to charge money for your software.
There, you're good.