Seven shops have been caught out selling cigarettes, alcohol and fireworks to children.
More than a third of shops visited by volunteers aged 15 and 16 were found to be prepared to sell the products to under-age customers.
The investigation by West Sussex Trading Standards and Sussex Police found four shops in Worthing and three in Bognor operating illegally.
Trading standards officers said in some cases no questions at all were asked of the volunteers let alone requesting proof of age.
It is illegal to sell these products to those under 18 and Trading Standards supports the Think 25 policy encouraging traders to ask for ID from anyone who looks under that age.
Christine Field, West Sussex County Council cabinet member for public protection, said: “What is an especially worrying development is the sale of fireworks to our volunteers.
“In the past this has proved very rare. However, in this exercise two shops sold both fireworks and cigarettes to the volunteer in the same purchase.”
Anyone suspecting a shop of serving under-age customers can report them anonymously on 0845 404 0506 or via www.westsussex.gov.uk by typing “incident reporting form” into the search bar.
See the latest news headlines from The Argus:
- Four men jailed for arranging prostitution of Brighton 16-year-old
- Bus company to review policy of allowing passengers to board its vehicles with hot food following passenger's 20 minute stand off with driver
- Disabled man fighting for life after street attack
- Boy left "shaken" after stranger grabs him in Tesco while he looked at Easter eggs
- Man repeatedly gropes woman as she tries to walk home