Alan Morris took the items and tried to blame their disappearance on other contractors who he said were carrying out the repairs.
But following an investigation by Strathclyde Police and South Lanarkshire Trading Standards officers, Morris pleaded guilty at Hamilton Sheriff Court to the deceptions.
He admitted 13 charges of theft of jewellery, totalling £94,352.
The 55-year-old, from Clarkston, East Renfrewshire, will be sentenced next month.
Morris, who traded from Figaro jeweller's in Quarry Street, Hamilton, had agreed to repair a wide range of items, including watches, rings, bracelets and necklaces, but these went missing.
He then falsely blamed other jewellers he had subcontracted to carry out the repair work for the problems.
Police and Trading Standards launched an investigation after dozens of fed-up customers complained about the missing articles.
About £19,000 of items were recovered and returned to their owners.
As well as being prosecuted for the theft, Morris was also the subject of enforcement action by South Lanarkshire Council Trading Standards under the Consumer Protection from Unfair Trading Regulations 2008, and the Enterprise Act 2002.
David Templeton, divisional Trading Standards officer for South Lanarkshire, said: "Crucially, our action prevents him from continuing criminal activities.
"The Enforcement Order not only safeguards the economic interests of consumers but also protects the local economy by tackling rogue traders."
Morris had initially provided an 'Undertaking' – a written legal promise – to Trading Standards to stop using unfair trading practices against consumers.
When he persisted, and subsequently breached the Undertaking, Trading Standards successfully obtained the Enforcement Order at Hamilton Sheriff Court.
The Order means Morris must stop using unfair trading practices.
Should he defy the Order, he could be found in contempt of court.