Prime is a subscription model, and is twice as much as Costco's.

It's also optional though, Costco membership isn't.

Why would you shop at Amazon as a non-prime member? If you're going to be sold knock-offs and returns sold as new products, you might as well get some videos and movies to watch for the hastle.

Edit: you can also find a friend with a Costco membership and go with them. It's not like it's that exclusive.

This is actually a good point. Amazon is only able to sell that cheap crap because their return policy is so good. Without prime you literally might as well just order the stuff straight from china.

And to be fair, Costco worked a lot better for me when it was in the general direction of where I work.

And a long with that, why would you buy from Amazon without Prime, and deal with slow, non-free shipping, when many competitors (Target, Walmart, etc.) have upped their game and offer 2-day shipping with a relatively low total purchase amount, with no membership fee needed?

I wouldn't recommend a costco subscription unless you grocery shop there.