A suspected illegal immigrant was arrested during raids across Sutton on Friday.
The operation saw the South London Home Office Enforcement Team, Trading Standards and the Metropolitan Police, swoop on restaurants and shops in an intelligence-lead operation called Operation Condor.
At Euro Foods and Wines on Bishopsford Road, Sutton, a man who denied working at the shop, despite serving a police officer moments earlier was arrested on suspicion of entering the country illegally.
Trading Standards issued a warning to the Post Office in Hackbridge after the owner failed to display prices of his goods. Jason Hitchcock, one of the borough's Met Police licensing officers said failing to price goods means there is scope for people to be ripped off.
He said: "In some places, shop owners make up prices as they go along. If you are wearing a tie you will be charged more for something than if you are wearing a t shirt. If goods are priced properly, people know what they should be paying for something. I've heard an old lady being charged £15 for shopping one week, and then £20 for exactly the same shopping the week after. It's not on."
The shop now has two weeks to rectify the problem before Trading Standards revisit.
At Belmont restaurant Haweli, one man, who denied being a member of staff, made a run for the door as the agency's arrived. The owner of the restaurant told officers the man did not work there and was just visiting. All the members of staff claimed to be enrolled on a college course, which means they are only allowed to do 20 hours a week.
The restaurant was fined £30,000 in 2007 for having illegal immigrants working on site. Licence holders can be fined £10,000 per illegal immigrant working on their premises.
One member of staff was arrested.
Jill Smith, from the Home Office Enforcement Team, said: "We see a lot of foreign students working in restaurants. Sometimes they are legitimate students, but we see a lot of people enrolled on courses who work full time when they are only supposed to work 20 hours a week."