Wal-Mart does not double coupons, but it will price match for the exact same item. Just bring your ad with you to the checkout counter and show it to the salesperson. Keep in mind that Wal-Mart practices regional pricing. This means that the prices at one store may be slightly higher or lower depending solely on where it is located. If you can find a better deal in another city, bring the coupon or ad to your store.
Wal-Mart does not accept double coupons from consumers. They do however accept coupons and in some cases will issue change back to the consumer if the price of the item is cheaper then the coupon price.