Commissioner Anna Rawlings said in a statement Middleditch had "traded off Hebel's premium brand name while knowingly supplying generic substitutes," giving him a financial advantage over competitors.
However in a statement, Middleditch defended his actions and said the clients involved were not disadvantaged, and that one remained a loyal customer.
"I did not intentionally mislead any clients over the use of the Hebel brand in 2013," he said.
Rawlings said the Commission prioritised cases involving building materials because of the potential significant harm could cause consumers.
The prosecution is part of a wider case involving four individuals associated with Cavan Forde Group, and also allegedly involving the misrepresentation of the cladding as a Hebel product.
In October 2017 Christchurch Lightweight Concrete owner and director Darryl Campbell was fined $151,875 for his role.
Two other defendants have pleaded not guilty and will go to trial.
Both Christchurch Lightweight Concrete and Supercrete Auckland are no longer in operation.