Where lies the line between a sting operation and entrapment? I imagine that it's the point where a crime wouldn't have happened if the controlled situation' wasn't there. A car thief trying to steal a monitored car is in my eyes legal but the police asking people to commit a (small) crime certainly isn't.

In Belgium sting operations in itself are illegal because of the same reasoning above. The car thief wouldn't have stolen that car if it wasn't there. This doesn't take into account that the person could've been 'on the hunt' so that the thief still would've committed a theft.

I prefer the sting operations as a legal instrument for the police, however with a judicial branch that keeps a close eye on whether or not the police tricked the accused in committing a crime.