What? No way. This is absurd.
Its like someone based their game source on the Quake, FarCry or even Unreal.
Taking the mechanic, source code, with just little altering, and just re-skinning it.
What kind of world are we living in??
Oh wait...........
Sarcasm aside, mackbanville, its better just create your casual game from scratch rather than buying them, its much more satisfying, it'll save you some money, and you learn more from it. Most of the ones they sell on those sites are just a simple game mechanics, that probably will just take you couple of weeks to create.