I run a shop with a lot of non mechanics doing the initial bicycle inspection. One tool has helped, The Park Chain Checker. They are told that when they see .75 in the inspection window that they should tell the customer the chain is worn out and the cassette / freewheel should be replaced as well. I have instructed them on how to feel loose bearing in the hubs, headset, and bottom bracket. I have shown them examples of worn tires, worn brake pads and bent rims. I have them put each bike up in a stand to check the function of the shifters, and all cables.
We have a little check off list for them to go through. This has helped.