One of the things that bike shop employees tend to do is to assume that customers know how to use their equipment. The guys (and gals) who work in shops ride bikes constantly, and they read about bikes, and new equipment, all the time, as well. So, when a customer comes in, they assume that customer at least knows the basics of operation on whatever they are looking for.
The classic example of this is the Shimano STI shifters. On those shifters, the rear derailleur shifts up or down almost immediately when the shifter is activated. Click-shift.
But, on the front, it's necessary to push the lever, and keep it pushed while the chain finds its way onto the next chainring. The rings have shift zones built into them, and the chain will only move from ring to ring at those spots in the rings' rotation. Sometimes, you will hit the shifter just as the shifting ramp comes around, and the front will shift like the rear.
Most times, it won't. But, no one thinks to tell the customer that.
So many times, as the Service Manager, I had customers bring back a brand-new bike because "it won't shift". It took me a while to see the pattern. After test-riding it, myself, and telling the customer that it worked perfectly, they would ride around the parking lot and tell me it was still broken.
After a while, I didn't even bother to adjust anything, or ride the bike, myself. I would just get my bike and say, "Let me ride with you while you shift the bike."
Then, as we rode, I would tell them how the front shifter was supposed to work, they would try it, and suddenly the bike would be fixed. I could never seem to get the majority of the sales guys to do this, as they sold the bike.
And, it wasn't just our shop. Bikes from other shops came in, with the same "problem". But, that was okay, really. I got to be the one who solved the problem for the customer.
Jon Grinder, Knight in Shining Armor...