I worked at a hardware store with similar problems.
The one that I noticed the most was the entire interface was driven by shortcut keys, although there was no on-screen reference to which key to press, in what order. And they didn't have any real resemblance to their function. For example a to begin a trade sale you pressed 's' or a normal sale was 'b', and you could invoke a staff discount by pressing 'r' during a sale. When the woman in charge of the front counter was fired for shoplifting(...) the young staff were screwed as they didn't know how to process most sales and the manual was lost decades before
The other was the guy out the back processing inwards goods (directly on the server) but to find out the sku for each item he had to begin a sale and scan the item, write down the sku, cancel the sale, log out then log in to the server as admin (he couldn't have 2 sessions open at once), add the new goods then start again for the next product. On a busy day he would scan a few sku's at a time but I got the feeling he didn't request it to be changed for job security.