If I request 1/4 of a yard - I am, of course, happy to get 'extra - but if it's 9 inches long - WOF - I'm in no position to complain.
I usually do buy extra - to allow for shrinkage or wonkiness caused by the fabric being put on the bolt askew. But it isn't up to the store to 'compensate' for what the fabric does after it leaves the place.