He made plans to meet to buy contraband cigarettes - but changed his mind and decided to steal them instead. Former logistics coordinator Guan Qiuqiang, 29, then punched the seller's face when the latter tried to take his photo.
The seller called police and officers arrested Guan, who continued dealing in contraband cigarettes while out on bail over the incident.
Guan was jailed for two years and eight months on Tuesday, after pleading guilty to three counts of dealing in the cigarettes and one count of causing hurt.
Three other counts of dealing in contraband cigarettes were taken into consideration during sentencing.
The court heard that in December 2015 and November last year, Guan illegally dealt in 525,920 sticks of cigarettes in 2,624 cartons and 56 packets.
They were worth more than $292,000. In all, the duty unpaid was $204,056.96. Guan did not pay the $20,467.32 of goods and services tax either.
On Dec 22, 2015, Guan and two friends planned to meet the seller at the void deck of Block 412, Ang Mo Kio Avenue 10. While on the way, Guan changed his mind and decided to steal the items from him.
When they reached their destination, one of Guan's friends tried to scare the seller away so that his companions could steal the wares.
The seller ran away but returned soon after and tried to snap a picture of Guan with his mobile phone.
Deputy Public Prosecutor Kenneth Kee said: "The accused tried to prevent the victim from taking his photo by pushing the victim's phone away.
"With intention to cause hurt, the accused then punched the victim once on the left side of his face."
When the police were alerted, officers who turned up found 181 cartons and 40 packets of contraband cigarettes at the void deck.
While he was out on bail, Customs officers caught Guan dealing with 1,982 cartons and 16 packets of contraband cigarettes in Buroh Crescent, near Boon Lay, on Nov 11 last year.
Five days later, officers caught him dealing in 461 cartons at a substation in Yishun Avenue 11.
The court heard that Guan had ordered the cigarettes from a supplier in China and intended to sell them for a profit. There were no details on how he ordered the cigarettes.
Customs Prosecuting Officer Josiah Zee said the seller whom Guan assaulted has absconded and a warrant of arrest has been issued against him.
For assault, Guan could have been jailed for up to two years and fined up to $5,000. And for dealing in contraband cigarettes, he could have been jailed for up to three years and fined on each charge.