An experienced rider can usually tell in a very short ride that a bike fits right because they know the feel they are looking for. Newer riders should not consider a test ride 1 lap around the parking lot. You need to ride for an hour or so to know how it really feels to you. You are more likely to get it close if you know all your measurements, not just height, and can provide them to the LBS. That will allow them to hit the first guess pretty close. If you are test riding and need something adjusted differently then the test starts over with the adjustment. Most bikes will fit one size above and one size below ideal. You can make adjustments like stem length, seat position, bar width .... to dial it in.