Question

A broker pulls up in front of the next home to be shown to the buyers and, at first glance, they tell the broker that they don't like the looks of the house, the broker should

Answer 1

The broker should call the listing office and cancel the showing as soon as possible.
Among the possible options, this is the one I would choose. The broker should try and convince these buyers to at least take a look at the house so as to evaluate and compare to their other options. If they still don't want to do it, then the broker should cancel everything and move on.