Surely that's a good thing? That's pretty much the spirit and purpose of open source software.

Sounds more like you want to call it open source but dual license for personal vs commercial use in order to make some money. Of course, this is fine, many projects do this, but in this case, there would be no interest in using for personal use - who's going to set up a gambling site that they run on their local machine to gamble against themselves? As soon as you allow others to gamble, it becomes commercial.
The other problem if you try to dual license is that the open source libraries that you use in building this project may no allow relicensing.