Coupons to mess with the system

Within a single day, thousands of customers use up their coupons on purchases at the POS and many times these coupons aren't even applicable to the items they picked out.  Nonetheless, from what I learned thus far, these coupons are taken, the items are scanned, and the customer leaves happy.  Why?  Because the customer always has to leave happy.  Satisfied.  Content.  Merry.

Apparently, it doesn't matter that the store registers a coupon to the incorrect item.  The store still makes money off the purchased good but instead it is the manufacturer that issued the coupon [and corresponding item(s)] that loses money.  How so?  Well that's because the manufacturer [still] has to reimburse the store for the coupons said-store printed out in the weekly flyers.

With that in mind, I'm surprised that there are a lot of smart customers that utilize coupons very well to get the most savings out of their purchases.  However, I'm also flabbergasted to know that some of these customers know fully well that they are also cheating the system [by intimidating the cashier into accepting coupons that shouldn't be accepted].    Wait a moment.  Huh?

From further reading, it turns out that some customers cheat the system by applying as many coupons to particular items that they ultimately become "free" in a sense and also provide monetary returns.   For example:

Customer buys 6 Tide Detergents for $5.00 each.   (that should be $30.00 before tax right?)
Customer brings 6 coupons for $1.50 off each Tide Detergent.  (that's $9.00 off)
Customer brings 6 manufacturer coupons for $1.00 off each Tide product.  (another $6.00 off)
Customer gets a $5.00 gift card for every 2 Tide Detergents purchased.  (that's $15 in gift cards)

When you factor the price in.  -$30 before taxes for Tide Detergents + $9 +$6 +$15 = $0.00 total.
Now of course if the MFR coupon was $1.50 off instead of $1, then they'd essentially make $3 in profits.  So this method of working around the system can easily be done if the shopper is smart enough to plan ahead and purchase enough to make the items in essence "free", but apparently it's also somewhat "illegal" to do.

First, most coupons only apply to one item or one single transaction.  Some also only apply if you purchase a combination of stated products.  However, because customers always leave happy, these crafty customers intimidate the cashiers into accepting the coupons foregoing the fine print.  Most of the times, these kinds of customers are the type to purchase many items (15+) and also bring with them many coupons.  Then again, I think there's only a handful out of the thousands of customers out there that are keen enough to pull this off on a regular basis.