He said some stores employed "vanity sizing" - labelling garments a size smaller than usual - to flatter a customer into buying.
"Marketing and sizing work together sometimes," he said.
"It's about engaging someone in your brand by having someone fit into a smaller size. It does happen."
There were no "standard" sizes in New Zealand - or anywhere else in the world - which left the decision of what a size 10 looked like up to the designers. He said he would support moves to make sizing more consistent, but conceded it was unrealistic in the age of the "global economy".
Australian design and fashion researchers discovered that an average size 10 had increased a huge 15cm since the 1970s, when a size 10 woman would have to have tiny 80-60-85cm measurements across her bust, waist and hips. Now it is 95-75-105cm.
Fashion Industry NZ executive officer Mapihi Opai said the actual fit of a garment should take priority over the number on the label.
Clothing brands meticulously developed pattern blocks for a specific target audience and their customers returned because that fit worked for them, she added.
"The argument against standardised sizing is that the human body doesn't come in a standardised form.
"Most people don't conform to a very precise set of measurements. We're not built like mannequins," she said.
