The agent suggested I request an inspection of my bike suitcase in my presence, after which, my suitcase would be tagged as having already passed inspection. When I checked in at Washington-Dulles, the agent didn't know what I was talking about. However, another agent overheard me, and she told my check-in agent that she was authorized to do such inspections.

That implies that on American, at least, some employees are authorized to do security inspections and others are not. So, I let her check me in. She was very thorough (she wouldn't let me pack my Tri-flow chain lubricant), and when she was finished, she placed a special sticker on my suitcase, and wrote her own ID number on the sticker. She advised me to lock the suitcase at that point, though I chose not to.

Both of our bikes arrived in Guadalajara in fine condition. My friend had to pay $50 for his bike, plus $20 for the box. As we arrived at GDL around 10pm, we took a camioneta taxi into the city. It cost a fixed rate 130 pesos, plus about 50 additional pesos for my friend's bike box. A paqueteria kindly let us store my empty suitcase and my friend's empty bike box for free (the hotel refused after saying OK on the phone).

When I returned home, random inspections were done only prior to check-in, on tables near the check-in counter. I wasn't selected, but I expressed my concerns to my check-in agent and opened up my suitcase, and he told me there were not random inspection AFTER check-in in Guadalajara, so I needn't worry. After clearing customs in Dallas, the American agent who I re-checked my suitcase with said there were no additional inspections of luggage that cleared customs and were re-checked in. It arrived at Washington-National unscathed.

BTW, Mexican buses readily accept bicycles. No hassles at all. Sometimes there is a charge, sometimes not. Often a tip is expected for the baggage guy who supervises loading, even if you load the bikes yourselves.