Interesting - Part of me wonders about what their accuracy rate was with that kind of system. 1,000 different 3-digit numbers is still a lot to remember. It's possible, but it would seem to add a pretty big barrier for a lot of people who would otherwise be fine as a cashier, elsewhere. Though when I worked at CompUSA in the early 90s, we lacked barcode readers and each product had a 6-digit SKU which meant only being able to remember a handful of them for the most popular products[0]. It was also horrible for accuracy because each SKU was assigned in order, so fat fingering any of the numbers would result in the wrong product being rung up. This was often caught, but if it was the last or second to last digit that was missed, it was likely to end up being a different version of the same product (more RAM, different CPU, etc) and it would be missed[1] resulting in either the customer paying more (unlikely - those were not missed) or paying less (likely, because the cashier wouldn't notice and the customer was less likely to say anything if they happened to actually notice and the result is them saving a few hundred bucks).
[0] We did have one cashier that I'm fairly certain had well over 90% of the products in the store memorized (we'd grab random things trying to throw him off, but he was like a machine). He had brain surgery a decade prior or so and said the way his memory worked changed shortly afterwards.
[1] The worst case I recall was a $500-$600 memory upgrade kit for an Compaq laptop that was fat fingered, resulting in the generic being rung up. It had an identical description but was half the price. A few days after inventory was done, they traced it back to a single customer who bought every one we had in stock in one transaction. The customer probably knew the price was way too good and decided to buy them all as a result (it's unlikely even he knew it was a cashier error since the product looked right on the receipt).