Lincolnshire Police and Trading Standards sent out underage volunteers to buy tobacco and alcohol from 12 Lincoln shops and one of them failed the test.
Police have fined a shop worker £80 at Moonlight Shopper in Monks Road for selling alcohol and tobacco to a 14-year-old girl and a 15-year-old boy.
A total of 12 shops were tested on January 15 using the same teenagers and Moonlight Shopper was the only business that sold to the youngsters.
Lincolnshire Police Chief Inspector Mark Housley said he was happy 11 out of 12 shops passed the test.
“It shows the vast majority of retailers in the city are trading responsibly. We’d like to thank them for that and urge them to continue.
“The fact that one shop failed suggests there’s a minority of traders out there who need to improve standards.
“We know that antisocial behaviour is one of the main concerns of people living in the city and underage drinking is one of the root causes of a lot of the problems we face.
“We make no apologies for positive action like this and it will continue throughout the New Year.”
Trading Standards Divisional Manager Graham Killick said: “It’s reassuring to see that only one business failed the test, suggesting the message about underage sales is getting through.
“Trading Standards continues to help businesses stick to the law by advising on good practice such as a Challenge 25 Policy, keeping detailed training notes and having a record of refusals.”
Some of the shops that passed the test on January 15 are One Stop on High Street, two international food stores on Portland Street, and Bargain Booze on Monks Road.