It is always a great idea to have a copy of a store's coupon policy with you.
Once, I was doing a huge buy at Target with almost 100 coupons. I shop this Target all the time and never have had an issue. On this particular day, if I had not have had the policy with me I would not have been able to save over $400.
I try to remember to print every other month, so there is a recent date on the policy.
Here is a link to the policies of several stores. Want one added to the list? Put the name of the store in the comments.