Manufacturer coupons follow a GS1 standard in North America. It encodes values such as deal amount, if it’s a percent off or dollar off, minimum units required, if the coupon will work for a specific UPC or it works for the entire manufacturer, expiration date, etc.

Most point of sale terminals only verify that the data is the correct format; it does NOT validate or authenticate. The cashier should act as a second check (theoretically a barcode printed on toilet paper for 100% off a TV would work for instance). The coupon gets collected and sent to a 3rd party clearinghouse 95% of the time. That clearinghouse will check for fraud and authenticity, and invoice the manufacturer on behalf of the retailer at the end of a month.

Source: Led marketing for multiple CPG/Food companies, lmk if other questions, I don’t often get to talk about this on here!

> Most point of sale terminals only verify that the data is the correct format; it does NOT validate or authenticate

This sound like a major design flaw though doesn't it? I would assume that the system would actually check whether this particular product is eligible for that discount instead of accepting it blindly? Why is one potential API call moved further down the chain to 'clearinghouse'? Why is this process 'failing' so late in the chain?

Grocery is really behind on technology. In fact if you do direct to store delivery as a smaller farm/food manufacturer, most orders are placed via text message from the buyer to a sales person at the manufacturer.

There is very slow movement around a standard digital coupon format, that does allow validation. The biggest challenge is all parties need to work together to make it happen. Both the investment to update point of sale registers and then trying to get every grocery chain/store signed up to said format on one end, and then consumers actually using these coupons on the other (which require smartphones and app downloads currently). (https://www.gs1us.org/upcs-barcodes-prefixes/additional-ways...)

The uptake into digital coupons is still extremely slow; In 2020, the load-to-card type coupons you may have experienced are only at 30% of the coupon market.

Major chains predominantly run on Toshiba SurePOS 4960. That 4-digit number should give you a clue. It is, of course, a spinoff of an IBM monstrosity originating in 1980s.

This thing is programmed in REXX and Java. Many files end in .286

Although there are possibilities for API integrations, users usually use the ssh interface into the controller system. It would take significant effort to add manufacturer coupon validation logic.

By encoding self-contained data, coupons violate the first principle of data security - never trust the input.

Source: I service 4960 controllers for major chains. My first encounter having to edit REXX files using native tools was very interesting.

(Old) Coupon barcodes are fairly standardized.

https://fabulesslyfrugal.com/coupon-bar-codes-decoding-code/

Seems like the barcodes encoded the deal, and they figured out how to insert arbitrary discounts and resell high value products. You can find legitimate arbitrage opportunities with extreme couponning, but just like mechanical turk or ad view / click rewards "work" it very rarely reaches minimum wage when you account for time and profit. If people are making bank doing seemingly trivial stuff like this, it's going to be temporary and/or illegal.

I think it was in the early/mid aughts when grocery stores wised up. Couponing was a big deal during that time frame and I worked in a grocery store in the States at that time that would periodically do "double" and "triple" coupon weekends. We would have people walking out with $200-300 worth of merchandise on the triple weekends and they would have to scan a candy bar at the check out so that we didn't owe them money. It was always a cart full of pretty bizarre stuff that didn't look like a typical grocery trip in strangely large amounts (stuff like 4 bottles of Windex). They eventually stopped doing the double and triple coupon weekends once they figured out how much money they were losing.

That was also before you could easily just walk into a store then turn around and sell what you bought online two hours later too.