I do some couponing, I could help you if you like, and I can tell you a little about what they do, which to me doesn’t seem that realistic.
They match coupons with sales. Now, the stores the go to usually allow “overage”, double and triple coupons, matching sales. competitors coupons, etc… I don’t have any supermarkets around here that allow all of those, and a lot of people I have come in contact with don’t either, so that kind of raises a flag for me, but anyways… A lot of them order a bunch of coupons online and match it with a sale, often with the coupon being worth more than the price of the item. I am going to give you a made up example of one shopping trip. They order 100 coupons online from a “clipper service” for $.50 off mustard (which they had to pay money for if they got their coupons that way), and then go to the store that has double coupons going on and has them on sale for 69 cents a bottle and if the store allows overage (and allows them to buy 100), its like getting paid $31 for the mustard and they use that money towards other items (and in some stores tax). There are a lot of ifs involved. Then they buy 80 bottles of gatorade with a coupon that was buy one get one (often purchased online too), and since the store had the same sale, the coupon gives you the one you had to buy free, so two free bottle for every coupon. Say the gatorade was originally $1 and, then you saved $80 and the mustard was originally $1 before the sale, you saved another $100. Then you buy 50 boxes of mac and cheese for 10 cents a box with double coupons and sales, and 16 boxes of cereal for $1 each after coupons and sales, and that gives you another $45 savings for the mac and cheese and $32 savings for the cereal, and so now you have saved $237 and although the mac and cheese cost $5 and the cereal $16, you had $31 left over from the mustard, making your groceries free.
So now you can have a meal of mustard, cereal, mac and cheese, and gatorade 
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