No, a broker should not profess to be a space planner but he/she should be able to give you a general idea of how much space you probably need. This will certainly narrow down your search and eventually save you lots of money over the years.
Take a quick look at one of our other chapters to get some insight into exactly how to build a space model.
Your broker should be able to assist you in this. What ever you do, DON'T just tell your broker to go find you space based on some "in your head" calculation. Planning will really pay off in the savings.