A 16-year-old was sold lighter gas by a Thurso retailer during an undercover operation.
Cardosi’s shop in Princes Street fell foul of the law which states it is an offence to sell cigarette lighter refills to anyone under the age of 18.
The test purchasing exercise was carried out following concerns raised by NHS Highland’s Youth Action Service and the Caithness and Sutherland Drug and Alcohol Forum over substance misuse in the area.
Trading standards manager Gordon Robb said: "I am of course disappointed that the message about the sale of abusable solvents, including specifically age-restricted products like gas lighter refills, appears not to have got through to some people."
Shop owner Brian Cardosi is "dismayed" at the incident involving the volunteer teenager.
"I am disappointed that a member of my staff sold to the youngster but, ultimately, the buck stops with me," he said.
"It shows that even though you know the law and inform your staff it is easy to become complacent."
During the exercise the 16-year-old was able to purchase glues from four other retail outlets in Caithness without being challenged as to their purpose.
Mr Robb said: "Although there is a specific age restriction of 18 for the sale of gas lighter refills, there is no age restriction on the sale of other abusable solvents or volatile substances.
"With these products, it is an offence for a retailer to recklessly sell to a person of any age knowing that the substances will be abused."
*See more on this story in Wednesday’s Caithness Courier.