Know your restrictions!

Because the store gets reimbursed by the manufacturer, you must make sure that you use the coupon on the correct product and the correct size, otherwise, the store will not be reimbursed for the discount given to you. If the coupons specifically states that it is for the 40 count Hefty garbage bags, don't try to use it on 45 count, even if the coupon works and does not "beep" at the register.
Each coupon states on it the redemption rules.

Per purchase vs. per transaction
There is a lot of misunderstanding regarding the wording on a coupon regarding this issue. Per transaction is the same thing as saying per receipt. A transaction consists of as many items as you want to purchase on one receipt. If a coupon uses the wording one Per Transaction, that means that you will need to make many different transactions at that store to get multiples of that item.

One Per Purchase means that you can buy (purchase) as many of that item as you have coupons for. For example, If you have 4 Kraft salad dressing coupons, you can purchase 4 dressings, but you cannot purchase 2 dressings and try to apply all 4 coupons to the 2 dressings. You can only use 1 coupon per item purchased, unless otherwise stated on the coupon.

Per household vs. per person

If a coupon states One Per household, this includes anyone living at your address.

One Per person is the same thing as saying per paying customer. This means that you (yourself) can only purchase 1 of that item. However, your husband/wife may also purchase that item in a separate transaction as yours. They are another customer.

*Be aware that sometimes store cashiers and even managers themselves have no idea what the differences are in these wordings so be prepared on occasion to gently argue the point. In my experience, a bit of positive instruction usually goes a long way, and can change the managers understanding enough to make the next couponer behind you have an easier experience. On the contrary, getting flustered and being rude helps NO ONE! Remember though, that the store manager has the final say and can refuse to honor your explanation of the coupon rules. You can always try again later when you know that particular manager is not on duty. Sometimes that works and sometimes it doesn’t, but it may be worth a try.