By Sam BeckerFeatures correspondentAlamySelf-checkout technology has grown, but not every business and consumer is happy with the investment (Credit: Alamy)Unstaffed tills were supposed to revolutionise shopping. Now, both retailers and customers are bagging many self-checkout kiosks.It's a common sight at many retail stores: a queue of people, waiting to use a self-checkout kiosk, doing their best to remain patient as a lone store worker attends to multiple malfunctioning machines. The frustrat...