Mckinnon Heating Cooling

We asked McKinnon for advice about replacing the high-velocity vent covers for our townhouse. When enquiring about suitable vent covers and requesting a quote, I emailed a description of the HVAC system in our building as per status documents, and detailed pictures and measurements of the vent holes and the old vent covers – which McKinnon's owner also asked for, in order to be able to provide us with the right product.
As it turns out, the vent covers ordered for us by McKinnon are unsuitable for our system, so we asked to return them for a refund. After multiple attempts at contacting them about this issue over about a week, they eventually agreed to take them back but charged us a 15% manufacturer's restocking fee (a considerable amount, given the very high initial price of the vent covers). We eventually ended up purchasing custom-made, laser-cut vent covers for a fraction of the price.
I believe we did nothing wrong, as we were sold the wrong product: it is not our job to identify the part to purchase, or we would not have relied on McKinnon in the first place, and I provided McKinnon with plenty of details to come to the conclusion (before we did) that in fact they did not have the right product for us. I appreciate their help in trying to track down a product for us. However, communication and delivery arrangements were less than ideal. In addition, as McKinnon independently identified the most suitable product for us, and the product did not meet the requirements – both breaches of the terms of sale – we should have been entitled to a full refund.