I don't like it when I go into a music shop and I am made to feel like an idiot.
So many times, I walk into a shop and I get snorked at (usually by male staff) because I ask a simple question. I am a completely self-taught bass player and I don't read music, but that doesn't make me a retard. I've always just been able to listen to a song and then play it. Folks should never be ridiculed by shop staff for not knowing something. How else am I to find out if I don't ask? Needless to say, I would prefer to buy online than to be made to feel like a small child. If you have a shop that has friendly, supportive staff then you'd certainly get more customers like me.
And of course, range of goods, prices and honest staff are important too. People should be able to get something from your shop that they simply cannot get online. Help setting up guitars (I'd rather be shown how to do it than someone just do it for me!), showing newbies how to change strings, little extra freebies (picks, bags etc) are also good.
Good luck with the shop!