The FAR does this a good amount, and it's actually something I'm considering writing an article about in the coming months. If you look at the definition of "Commercial Item," it starts with the easiest type of commercial item to establish - the one the regulation directs reviewers to accept without much pushback - which include tables, chairs, laptops, etc. and ends with "nondevelopmental items" that have not been sold in the open market but were created at private expense and sold to state and local governments, etc.