Sure you can, you don't have to be a member to buy at Costco.comI understand why some don't like Amazon - but there model is built like Costco - you pay a membership. Difference is that without the membership you can't shop at Costco. I hate Costco actually - but we have a membership because I am married and the boss likes Costco.
They do have specials for club members only and only club members can buy in Costco warehouses.
I cant shop in an Amazon warehouse under any circumstance.
They are two completely different businesses.