Can WalMart Deny a Purchase?

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I don't know if this is a trend or just one store's policy but the WalMart where we usually buy our groceries has decided that they will ID EVERYONE who purchases beer or wine. Sure, they should make sure that underage people are not buying beer or wine. But why card people who are obviously over the legal age. Just imagine a 60 year old woman who no longer drives buying groceries and being denied a six pack of beer because she has no driver's license. Is this fair? Should a person always bring a friend with ID to the store with them, so that the friend can buy beeer or wine?