... then how much do you buy?
The question is one of straightness of cut and grain.
Supposing you've asked for a quarter-yard and the quilt shop gives you a 10" cut... and they're using a gridded cutting board and cutting straight across.
But, as we all know, fabric is often warped a bit when wrapped on the bolt, and it's not until after it is taken off the bolt and has a chance to "relax" that it springs back into shape.
So the question is... how much extra should the quilt shop be giving on each cut? Is the quilt shop responsible for the crookedness of the grain of the fabric? Or should the customer be willing to purchase a little extra, to account for this common problem? Is the answer somewhere in the middle?
How do you figure out what's right... when the real problem is with the wrapping of the fabric on the bolt, something which neither the customer nor the quilt shop has any control over?
(We won't even touch on the issue of fabric that's not printed straight on grain... that's a whole other topic!)