Tell your jobber he is a retard,the reason that the gun is sputtering is that it has an air leak.Put some thinner in the cup,take the lid off,hook up to an air line and pull the trigger with low psi(put on safety glasses)and see if there are air bubbles coming from the bottom of the pot when you pull the trigger.No pro in the world uses those stupid filters,I have seen more problems caused by those things.Check for a loose fluid tip or a worn baffle gasket.
Phone devilbiss customer service and they will help you out,number is on there website.
A lot of counter guys have never shot anything in their life. I can't believe he told you to put filters in it. Those filters are a marketing ploy. Do what C.C. said and yes, that jobber needs to find another occupation. I must have said it a million times; clean your gun and check all machined mating surfaces.Crazy Canuck- I will try that. I hoping to paint tonight.
Thanks for the heads up!!!