The CPO is done undercover and dairy owners did not know when the operation was performed.
People must be over 18 to buy cigarettes or synthetic cannabis. Retailers are required to ask for identification stating age before a sale is made.
Ms Poona said they usually have a mix of older and younger looking teenagers doing the test.
She said while dairy owners were found to be responsible, she had heard that some adults were buying the products for minors.
The sting, which is held every year in Wairarapa, helps keep people on their toes, she said.
"We are trying to protect the health of children in our community and having a legal purchasing age is one way of protecting their health."
Police can prosecute and fine retailers who sell the products to minors and adults who provide them to minors.
New laws coming into force in August will mean dairies, service stations, tattoo parlours and grocery stores will be banned from selling synthetic cannabis and other legal highs.
The Psychoactive Substances Bill will also require manufacturers to prove legal-high products are safe and will reinforce the restriction of the products to those over 18.
In last year's CPO, Wairarapa retailers passed the test with flying colours.