If it's good enough for Rufus Wainwright, Keane and KT Tunstall, it's good enough for you. They're just a few of the musicians who have played intimate in-store concerts at this Back Bay shop, full of brightly colored guitars mounted on the walls. Even if you're not a rock star, you can buy custom-made guitars (electric and acoustic), or at least test a few models out in the showroom.