Superintendent Sibonelo Mchunu, metro police spokesperson, said the gang was believed to be part of a syndicate orchestrating house robberies and hijackings in Westville since January.
An ADT security guard was also fatally shot when he responded to a house alarm being set off.
Mchunu said the mother of a one-month-old baby she was still breastfeeding, was among the seven suspects arrested during a police swoop in Clermont at the weekend.
The other male suspects apparently told police about renting guns from the woman.
Twelve guns were recovered in the sting operation - four from the woman and the others from the remaining suspects.
Mchunu said renting guns was a recent trend among criminals.
“Many cases have been lost due to the rent-a-gun culture. And this is why they love it,” he said on Wednesday.
“The person who rents out the weapon can say they were in hospital when a crime occurred and they can produce records to prove it.
“This creates a reasonable doubt, which forces courts to throw out the cases,” said Mchunu.
The recent arrests, however, did not mean that their policing initiative in Westville would come to an end.
Mchunu said this could be the tip of the iceberg and further arrests were expected.
Criminal experts argued that police would have to be more vigilant when investigating because of the gun-renting modus operandi.
Local private investigator Rick Crouch learnt about the trend a year ago.
“They can rent an AK-47 for about R100 to R150,” he said.
Renting the gun meant criminals might not be caught in possession of the weapon, he said.
However, Crouch added that if someone was caught with the rented firearm, they could be charged with all the crimes committed using the weapon, even though they might not have been involved in the crime.
The person renting out the firearm would be in a similar situation.
Crouch said rented firearms were generally used for house robberies and low-level crimes.
Syndicates and criminals involved in organised crime normally used police and military weapons, he said.
Asked how this could be prevented, Crouch said: “The police have to do their jobs.
“There were large amounts of police firearms that went missing and nobody was prosecuted for it.”
Criminologist Professor Rudolph Zinn also called for more thorough police investigations.
“Police should take note of this gun-renting phenomenon and be more aware of it.”
He said getting details from suspects and witnesses early would help because this would prevent the cases being thrown out of court.
From extensive interviews he had conducted with convicted criminals, Zinn said the firearms could be hired from a number of sources - security guards, police officers or army officials.
But this was not the only method, Zinn said, because criminals also swopped weapons among themselves so that they could not be traced back to them.