It can be due to a number of factors, you touched on the first being their settings and devices, but it can also be due to the juice your buying may not have been Steeped as long as the juice that is in their testers. If you have a juice thats really lacking, put it in a dark drawer for a week or two and revisit it. Steeping helps to bring the flavor out in juices, and if its a fresh batch they received, it may not have had the time to mature to allow all the flavors to come out. Where as in the tester, its probably been there for a bit and has had time to steep and really bring out all the flavor notes. Like I said though, definitely play around with the airflow control and watts on your setup now, I am confident that with some experimentation on closing down airflow and progressively changing watts, you will find your sweet spot where you are getting the flavor you desire.