One of my pet peeves in a retail store is waiting in line to pay for my purchase, especially if there are several cash lanes that are unattended.
A new drug store was built close to my home a couple of years ago. They installed 4 cash counters which I thought was great. However, it is rare that they have more than one or two people working these cash lanes. Today, for example, at 4:00 P.M. on a Saturday, they had one cash open while the line up continued to build. At one point there were more than 8 people in line waiting to pay for their purchases.
As a I left the store--without making a purchase--I expressed my frustration to the cashier only to be told that they were in the middle of a shift change and if I would just wait a few minutes someone would eventually help me. I took my business to their competiton across the street!
I can accept a line up when all the cash counters are open and I know that scheduling is challenging in retail. However, if this is a reoccurence in your store then you need to take a serious look at it because many people will eventually take their business elsewhere.