Our shop has the same policy (no returns). I make it a point, like when you rent a car, to go over the entire bike with the customer prior to them leaving the store. After a bike is sold we hand the bike off to our service department where they do a final safety/bolt check and install any accessories that were purchased with the bike. I cover all the contact areas (many of which were highlighted in the photos) so the customer understands the condition the bike was in when it left the store. This way they can't come back and try to say the bike was sold damaged, scuffed or otherwise blemished.
I'm not saying that's what you're trying to pass off but it's a difficult situation. As you indicated between shipment, assembly, any previous test rides on the bike it's usually impossible the bike will be completely immaculate when you buy it. Should it be damaged? No, absolutely not.
Out of curiosity are you 100% certain that all of those scuffs were present when you walked out the door with the bike?