I've done instruction in heirloom type sewing. As long as a sewing machine had a basic zig-zag stitch, it was usable and welcome in class. I learned heirloom and cutwork before embroidery machines so older techniques could be applied. You can needle paint with a straight stitch machine, a hoop, and some patience.
I would assume that anyone who learned to quilt before automated machines should be able to teach on any machine.
There are generic outlets for machine parts - so some machines might be able to be fitted with a special foot or single stitch plate if necessary. I remember reading about those with zig-zag plates and nothing else, blocking off part of the needle opening on the plate with tape! Where there's a will, there's a way.
If the store also sells fabric, the store is doing themselves a disservice by limiting machines for quilting. I've hauled my Pfaff 2170 to stores that sell other machines.
FYI - I have an old book on machine embroidery done with the first non-treadle Singers! The stuff is fantastic. All kinds of lace.