Ugly truth?
I keep finding my plugin included in a theme released on themeforest - at least once per month.
Still, I haven’t sold any extended license for months…(theme authors should buy an extended license for a codecanyon plugin every time they release on themeforest a new theme which includes that codecanyon plugin, but most themeforest authors do not know this)
So the ugly truth is that everyone (with a few exceptions) will create a temporary account, will buy your regular license and will do whatever they like with your item (themeforest or other). Unfortunately.