I would call it a bust. Can not say entrapment if someone is willing seeking or buying illegal drugs. It's just tough luck. Depending on the drug, amount and if first offense may get off with only fines.
It's called oops!!!! I bought my drugs from an unknown source. Now I'm in big trouble. If You bought them that's a criminal act, you want to blame the cop ? he didn't force you with his gun to buy them.