While searching through different properties, make a checklist of each tour you went on. After you collect your first proposals from all the commercial property owners, let them all know that you're looking at other properties before you make your decision. There is nothing wrong with hinting that you have other properties in mind. It could help you get a better deal.
Prior to selecting a real estate broker, determine what kind of negotiating tactics they have. Much like you would interview a prospective employee, question their experience and training. Look for a broker who always adopts an ethical approach, has values and know where to get good deals. Request evidence of previous negotiations; both successes and failures.