There is no right answer. Every designer will have a different design based on experience, cost consideration, brand loyalty, and profit margin, and their pain threshold for getting call backs. Try to understand what is their design criteria and do they use software or by hand. How long have they been designing irrigation not just selling it? Is the person you met the licensed irrigator or a sales person?
It is not often you get a design from a contractor with out a commitment. It is hard for a nonsprinkler professional to understand much about the design process anyway. I am sure you have better things to do than learn a new discipline that is not easy for first timers. You just need to check references and see sample designs of other jobs. If you give a contractor the contract you should be able to see the design in advance and approve or veto the plan to make changes.
Good Luck