When I worked at WalMart back in high school and college I used to assemble the bikes, though most of them were done by an older guy that was a good tinkerer and knew how to do them right. Assembly was putting the wheels on, pedals, handlears, maybe some stickers. We didnt adjust shifters or BBs, or install forks and headsets or anything like that. While we were trained and given proper tools (I also grew up fixing my own bike as a kid), I could see how that could be left to a high school kid with a pair of pliers if there is no proper supervision.