Hi Susan. You're talking about the "Agency Agreement Form" that is mandated of all licensees by the NYS Dept of State. It's not a contract and that is so stated on the form. Simply stated, it informs you as to who the sellers broker represents (in this case) and it's not you.
You were given this form because you are not working with a broker. If you were, you would have already signed off on the form at first substantial contact with that broker. While it would be a good thing for you to acknowledge the brokers relationship in the transaction, you cannot be compelled to sign it. In my experience, the only people who balk at signing off on the form are those that not only are not working with a buyers broker, they invariably are just lookers, not buyers. and so it goes.