Your cashiers need to process transactions quickly and accurately to keep your lanes moving. Yet bad barcodes slow down the lanes and cause errors.
Here is a quick and straightforward way to determine the problem
Go in cash register reports.
Select in sales
Dissection Sales /Profitability for a given period
Now place here, say the past three months and run this report.
You will get a report that looks like this one. Now, look at the last row marked.
Now run down the list.
You are looking for dissections with high quantities, and low scan rates as these are the big problem here.