I bought a 10 speed from walmart "assembled" a few years back. The brake pads were loose, off the rim and cock-eyed and not adjusted. Nothing I did not know how to fix since I was 7 years old. Buyer beware!
I agree, but most people assume the bikes they buy are safe, which most are. I wouldn't know what to look for, except that I worked at a large bicycle company. I just read an article about a young man winning a $13m lawsuit against Shimano because the cables slipped out of the brakes. He is a paraplagic because of the accident.
We had many meetings at work concerning safety, especially after someone was hurt because of cracked welds, loose spokes, defective brakes, and the likes. All are dangerous. We had a good record, but since most of the bikes are either assembled outside the US or the parts are outsourced outside the US, you don't know what you are getting.