Our LQS "tears" the fabric across WOF, so no matter what the condition of the fabric on the bolt, you get an even yard or whatever measurement. I used to worry about stretching but the LQS handles decent quality and so if there is any stretching it is minimal.
I usually buy just a smidgen extra (1/8 yd. or 1/4 yd. if not sure) for shrinkage... I WASH EVERYTHING!! that way there are no surprises, esp. with color running or fabric that's been twisted-catiwampus on the cardboard.