If I were a shop owner/manager, my "formula" would be approximately one "free" inch per yard
1/4 yard - plus 1/4 inch
1/2 yard - plus 1/2 inch
2 yards - plus 1 inch
Then I would just basically factor in that "extra/free" into the cost.
So if the "sales" say I've sold 12 yards of fabric, I would know that 12 yards 12 inches were gone.
That might get complicated for the record keeping, though.
I'm weird - I get just as irked if I'm shorted on $1.00/yard close-out fabric as I am if I'm shorted on $12.00/yard fabric.
I'll also go to the store that cuts a 38 inch yard that charges $9.99/per yard before I'll go to the store that cuts a 35-7/8 inch yard that charges $7.99/yard for the same fabric. Which really doesn't make much sense, but that is true for me.
I have learned to check the grain-lines on the fabrics before I buy them.
I've found that even some of the LQS fabric appears to be off-grain - sometimes it will "straighten" when it's washed - sometimes not.
I still don't feel that it's up to the shop to compensate for possible shrinkage. I would hope that the shop would cull out the badly off-grain fabrics before putting them on the shelves.
I think many of us have come to EXPECT getting extra when we buy fabric.
We don't usually get extra when we buy anything at the deli counter or at the lumber yard or at the candy store.