You never want to go to Walmart without a copy of their coupon policy in hand. (It says YES YOU CAN USE INTERNET COUPONS plain as day.) If your cashier says she won't take your internet printable coupons, ask for the manager. If they still refuse, whip out your Walmart's Coupon Policy which is printed right from their own website here. If they still balk, whip out your cell phone and dial 1-800-925-6278 and let the Customer Service Representative tell the manager what Walmart's coupon policy is.
Walmart does not double or triple any coupons.
You can also price match at Walmart by taking other stores circulars in with you to prove there is a lower price somewhere else.