More than £50,000 worth of jewellery has been seized by trading standards officials in a crackdown in Birmingham.
Officials returned with a haul of 104 items from 21 shops in Washwood Heath, Bordesley Green and Handsworth.
Twelve pieces had not been hallmarked and 19 were lower carat gold than advertised – meaning customers would have paid well over the odds.
Other valuables, bearing fake trade marks such as Nike and BMW, were also seized.
Now legal action is now set to be taken against the firms, which cannot be named.
Birmingham Trading Standards operations manager Vir Ahluwalia said: “Hallmarking is one of the oldest forms of consumer protection.
“Jewellers selling unhallmarked items place consumers at risk by not giving them an absolute guarantee that their purchase is what it claims to be.
“It also gives the jeweller an unfair financial advantage over businesses which comply with the law and pay to have jewellery hallmarked.”
Mr Ahluwalia said his team was now writing to all jewellers in the city to warn them to comply with the law.
The new crackdown came after Birmingham Assay Office, which carries out hallmarking, was saved from the chop last October.
The historic office – the largest of its kind in the world – was due to be closed with 120 job losses in plans to scrap hallmarking.
But it was saved after the government decided to preserve the 700-year-old tradition.
The sale of gold is currently big business with prices running at record highs.
Five years ago, an ounce of gold traded at about £300 but today it is worth around £1,100.
The scrap gold trade in particular is booming, with gold items often worth more as scrap than new.