A police operation in Northampton has resulted in several £90 fines.
The Northamptonshire Neighbourhood Team along with the Northamptonshire Emergency Services Cadets have conducted the test purchasing operation.
Eleven shops were visited, resulting in seven passes and four failures.
A police spokeswoman said: "In the lead up to Christmas, alcohol sales increase and it is essential that premises are complying with the ‘Challenge 25’ policy."
The four cashiers who failed were issued with a £90 fixed penalty notice along with a letter being sent to the licence holder.
The other seven shops have also been sent a letter, letting them know they passed a test purchase.