Its important to understand all the aspects of frame geometry, not just the seat tube height. For instance, I ride frames ranging from 57cm to 62cm and they all fit the same in terms of cockpit length. You didn't even specify if it was measured center to center or center to top. Some dude on the internet telling you to ride a 53 cm is meaningless without any other information. A 53 center to center is about the same as a 56 measured center to top. Go with what the LBS advises, or at least take their advice more seriously that random people on the internet.