Andrew, Tell the guy at the store that it's a great idea to have jam sessions because it's a fantastic source of income. Dave- the guy at the music store I go to- doesn't have much time to play along because he's always so busy. Selling books, strings picks, tuners, everything you need. While people are there they go ahead and buy while they are there instead of waiting till later.
From the none business side it is a blast. We had pobably 20 people show up last night. 3 upright bass's. That was interesting. Ha