Mitcham,
Dont at all feel bad for what you did. The first thing that cashiers are taught when they are in training is to LOOK IN AND AT THE CART to make sure that there is nothing in there. If the cashier was not SMART enoough to see this big sheet cake on top the cart then Walmart needs to screen their employees a little better. I, as a consumer, do not get a discount for telling them how to do their job so there fore there is no guilt.
I am glad that your son had a nice birthday cake! Hope it was good and dont you dare feel the least bit guilty.

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Be careful what you wish for.....