Yes you need to purchase a membership to buy at Costco.
You have to pay an annual membership, otherwise you cannot enter to see or buy. You can enter with someone who is a member and he or she buys what you want and of course you have to reimburse the money to the person who helped you enter and buy. I don't think it is discrimination.
It's not discrimination. You can't enter a movie theatre to watch part of a movie before paying. You can't play on a private golf course without paying or a special invitation. Same deal here.
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