Police say eight shops in the Vale's town centres passed underage sales tests with 'flying colours'.
Youth volunteers visited shops in Barry, Penarth and Llantwit Major to help trading standards officers with a test purchasing operation on Wednesday.
All of the shops visited refused to serve alcohol and vapes to the young volunteers.
A spokesperson for South Wales Police said: "Police Youth Volunteers play a key role in providing us with the perspectives of the young people in our society, while actively making a real difference in our communities."