You can bring as many people as you want with you, if you have a membership. However, only the member is allowed to make a purchase; if your friends reimburse you afterwards for the purchase that is your own business. Also, the food court does not require membership and anyone can eat there.
I have had 3 other people with me and was welcomed with a smile
We go in as a family of 3. I have seen larger family's go in. I've seen 3 generations of family go in. So I am not sure what type of limit is there for one card. Kevin Lee's post seems accurate. Costco customer service desk would have the most accurate information though.
You can bring as many people as you would like with 1 membership. However depending on which cashier you get, they are supposed to only let the card holder use credit card. The non members can still buy stuff but they have to use cash. Also the card has to have the persons face on it. If the card holder is not present nobody is shopping at all. Again this depends on the cashier but that's the official rule.
I have brought in 2 and haven't had a problem. I don't know if there is a limit though
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