The teenager was showing unusual behaviour so his father confronted him. The boy told him that he was consuming an intoxicant and the shopkeeper was also selling it to other minors, police said.
The father approached the Patel Nagar Police Station and the officials gave him an idea, they said.
He visited the shop with his son and with a mobile phone recorded the accused selling the substance to minors. He submitted the footage to the police along with a complaint, they said.