When the item being procured is "obviously" a commercial item, you're fairly safe leaving the determination to a checklist approach with objective evidence included. This is a common sense determination - office furniture, Dell laptops purchased online, Microsoft office products, COTS software, etc.
If it's a commercial item with minor modifications, focus your narrative on (a) determining the original item commercial; then (b) explaining how the modifications don't alter the form, fit and function of the item.