They were younger and not as nice as his regulars, he said.
"I realised there's no point in selling it anymore, we were going to lose our regular customers."
He said that since the product had been off the shelves, customers had been in asking to buy it, and when they found out he no longer sells it, they got hostile.
"I had one guy who smashed our stand when I told him."
He said although the banned substances were lucrative for the family business, he would rather not sell them.
"I'd rather have our old customers who come in every day with $1.90 for a loaf of bread."
With the bill now law, strict labelling requirements mean the product must list the ingredients, and no shop can advertise, except at the point of sale.
It is illegal to sell the products to those under 18 years of age.
Anyone who breaks the law could face fines of up to $50,000.
Minister of Police Anne Tolley said police now have a tool in the legislation to help combat legal highs.
"These products have had a shocking effect on young people and their families, and up until now, frontline officers have had to deal with the consequences."
Northland police youth crime Sergeant Dan Cleaver said officers would be checking in on known stockists to ensure they are complying with the new bill.