I always rip for borders. It's accurate and so much faster. When cross-ripping it does distort the fabric edge a bit, but you can iron that back down and hide it in the seam allowance. Ripping does follow the grain, and is accurate.
Rather than lose you as a customer, Tartan, I'm sure any shop would be glad to comply with your request that they cut, rather than tear, your fabric purchases. Just ask them not to tear.