When a negotiator presents an ‘either or’ choice, he’s attempting to steer you down a particular path. That path, more than likely, is advantageous for him.
One way to combat his attempt to limit your options is to ask, what other options might there be? By posing that one question, it will allow you to gather additional insight from him.
He may not be willing to give you that insight, but observe his mannerisms and you’ll gain insight as to whether he does have something else in mind.
Worse case, he says he can’t think of any other options, at which time you tell him that you need time to think about his offer. Begin to exit from the negotiation table to contemplate other options that you might consider. Note his reaction to your withdrawal. That too will give you insight into his mindset.
Remember, you’re always negotiating!