Just because a person can do something doesn't mean they should. Just because a person can, by virtue of their membership, make an exchange for 90 days at Costco, doesn't mean they should especially for no reason other than them having the ability to do so.
You are missing the point though - you are talking morality and class but every time you walk in to a Costco store there a wall size sign saying - Costco will accept any item if you are not fully satisfied with it, Costco will also refund your membership fees a 100% at any time during the membership if you are not happy!
I actually saw people return partially consumed food, six month old furniture, old pc's, even used mattresses. A 60 days old phone is the least of their worries particularly when the customer is not happy since its a delayed phone that was bug full since day one.
You are saying he has not class or morality because he follows the store policy, i think you are wrong and that warrants an apology.