As you probably know, there is a lot more involved in fitting a bike than just inseam. Other measurements; torso, arm, blah blah blah. But you can "fit" a certain bike perfectly on paper, doesn't mean it's the right size for you. You need to find a way to get on one, feel it, ride it and say, "I feel a little cramped on this one" or "The reach is a bit too long" I'm 5'10 and ride a 19" that I think is a perfect fit. You may need to go to another shop if this one isn't willing to get you a bike in for you to try. Good luck.