.... the agent asked to search his bags. Rivers complied.
Well, there is your problem. Learn the following phrases:
1) I do not wish to be encountered
2) I do not answer questions from law enforcement or agents of the state without the presence of my attorney
3) I do not consent to any searches of my person or my property
4) Am I being detained or am I free to go
5) Since you have not clearly answered that I am detained, I am going to assume that I am NOT detained and will now be on my way.
6) Depriving me of my rights is a violation of title 42 section 1983 of the US code
7) I wish to assert my right to not speak to you or answer any of your questions.
And say nothing else.
Those are the correct responses. Thanks for listing them so clearly.