Almost half of all Scottish local authorities now have eight or fewer trading standards staff as tough economic conditions and the rise of internet shopping leave people more vulnerable, the Accounts Commission said.
The body, which monitors the performance of councils, said the long-term viability of trading standards services was now under threat, with claims that older people and low-income families are particularly at risk.
Accounts Commission chairman John Baillie said: "We're currently living in a period of economic hardship, the very time consumers most need protection and help. The longer-term threat to these vital services is worrying.
"Councils are having to cope with severe financial pressures. They need to work together to find radical new ways of delivering these services and establish national standards.
"They should do this as a matter of urgency before it's too late and they can no longer prevent risks to consumers. The public are entitled to expect a consistent standard of advice and protection across the country."
The report, Protecting Consumers, found trading standards services, whose key functions include educating and inspecting firms, resolving problems and enforcing consumer law, have lost a higher proportion of jobs in recent years than other departments.
Nearly half of councils now have so few trading standards staff that they may not be able to provide an acceptable level of service, the report found.
While food safety has lost fewer jobs, those in both services are concerned about loss of expertise and lack of trainee posts.
Both have lost nearly one-third of staff since 2008 through voluntary redundancies and turnover, with fewer workers replaced in trading standards.
An ageing profile of qualified trading standards staff and insufficient numbers of new staff has also been highlighted.
While there are about 620 members of staff across Scotland working on trading standards and food safety, staffing levels amount to little over one officer for every 10,000 people.
While consumers spend about £56 billion a year, just £21 million is spent by councils on trading standards and food safety.
The report added: "More people are shopping on the internet and this has introduced new risks, such as web-based scams or new sellers being unaware of consumer protection laws that allow people to change their minds about a purchase.
"Also, changes in consumers' and businesses' behaviour due to the economic climate have heightened some risks as people seek lower prices and some businesses seek to reduce their costs by cutting corners."
Tom Bell, chief executive of The Royal Environmental Health Institute for Scotland, said: "The report rightly points out what we have been highlighting for some time – the under-resourcing of environmental health services, poor succession planning and lack of training places."
Public service union Unison said the horse meat in burgers scandal also highlighted the importance of food inspectors.
Dave Watson, head of campaigns, said: "This is another example of the damage to vital public services caused by government funding cuts at UK, Scottish and local levels."
Cosla, the umbrella body for Scotland's councils, said: "Trading standards services in Scotland are providing consumers not only with excellent value for money, but also have the potential to grow stronger In these tough times, experience suggests we are all more than ever at risk from scammers."