I'm sorry I beg to differ with #2 above. You and your co-worker are traveling companions on a flight. As long as you are comfortable / trusting of his luggage contents and that he's not having you transport illicit goods for him, this is no different than family members consolidating baggage under the member with highest privileges. Or at least, not any different that UA needs to know.
You step out of the taxi holding colleague's bag. What is UA to know the difference?
actually, it was the airline check-in agent's suggestion... (a Star Alliance airline, not United) she weighed my friend / co-worker's bag which was a "little" overweight and suggested that it be checked as "my" bag... I figured that if she suggested it, then it must be okay? However, I just want to know if there are any rules against doing this. If there are, I'll just flatly refuse to do it next time.
