Walmart has recently updated their coupon policy. My advice would be to print the Walmart Coupon Policy and the Walmart Price Matching policy, read it carefully and be sure to carry it with you. If your couponing methods are ever questioned, you can easily pull out the policy. Also, if you do run into a problem at a store, be sure to ask for the manager and get the name of the manager as well.
You can always put your items back and call the corporate offices to voice your complaint if necessary. For me personally, any time I have ran into issues, I"I've simply called a manger and all was well again.