Question

You are at a concert and can’t hear your favorite band playing because the older person sitting next to you, who you do not know, is talking too much. How would you tell him or her not to talk (using the negative Ud. command form)? No ___.

Answer 1

You shoul always add "por favor" to your commands in Spanish.

Step-by-step explanation:

I will give you a list of examples:

¿Podrías cerrar la puerta al salir, por favor? - Could you close the door on your way out, please?

Por favor, ¿podrías apagar la luz? - Please, could you turn the light off?

Now, answering your question "how woud you tell him or her not to talk?" (using the negative Ud. command form).

Por favor, podría Ud. no hablar tanto?

No hable tanto, por favor.

Remember, in Spanish USTED (ud.) is more formal than TÚ, while in English the personal pronoun YOU works indistinctly; since TÚ is used with friends or in casual environments.

Answer 2

In Spanish you need to use por favor with the commands,
because is better and more polite.
More polite is ¿Podría callarse por favor? ¿Podría hacer silencio por favor?

Hope this helps