TRADERS targeted in three undercover operations in Kirklees shops passed the test when it came to not selling alcohol to children.
But they are being warned they will be prosecuted if they fail in future.
Consumer bosses said shopkeepers appear to be learning their lesson after they set traps to see if they would be willing to sell booze to under-age teenagers.
But West Yorkshire chief trading standards officer Martin Wood said the tests would go on and prosecutions would be launched if needed.
He said: "Any breach of the legislation will be treated very seriously. This service will continue to investigate any complaints where there is an allegation of age-restricted products being sold to children."
In the latest operations, Kirklees shops, off-licences and supermarkets were visited using teenagers trying to purchase drink.
Every shop refused to sell alcohol.
Clr Graham Clarke, chairman of West Yorkshire's trading standards committee, said: "I am delighted to report these results. It reassures residents that there are responsible retailers out there.
"I would urge all retailers to adopt the policy of `no proof of age then no sale'."
Trading standards staff are urging anyone who suspects shopkeepers of selling to under-age children to ring their hotline on 0113 3848 848.
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