Les is quite right about the person rather than the instrument etc. as a teacher of melodeon and accordion (button & piano) I teach new students/players how to play very quietly at a very early stage - that way they can practice without upsetting the neighbours!
I find it much harder 'converting' more experienced players into quiet mode!. My DG tutor book (available as buy now item on ebay -(just put in melodeon) has a section on playing quietly. If anyone is within range of Anglesey, North Wales, I can offer private lessons georgegarside@talktalk.net.
To play quietly needs highly developed bellows control, using the wrist rather than the elbow to control the ins & outs.This largely eliminates the heavy tugging & shoving of the bellows that by its very nature reduces all chances of any degree of finesse. ~A fidler does not attempt to saw his instrument inhalf with the bow!!