DULUTH, MN—Angry about the convenience store's poor service, Dina Jorgenson abruptly stormed out of Marvin's QuikStop unseen Monday. "Oh, I've had enough of this," Jorgenson said, pointedly slamming her passion-fruit Snapple on the counter and marching out the front door, after having waited in line for nearly 10 minutes. Two hours later, QuikStop cashier Tasha Quiggle asked a fellow clerk why there was a warm Snapple sitting on the counter.