And without painless returns, Amazon loses a lot of appeal (over the high street, John Lewis online, etc.) for me.
If somebody put something bad into the supposed-to-be-fungible warehouse pool, and I'm the unlucky recipient, then that's one example of where the better customer service comes into play.
If you buy sold by BESTWAREZ-FOR-U and despatched by Amazon, then you get it shipped from the same pool but crapper service when you get the same amount of unluck and receive the dodgy one. (And if it's despatched by them and you've not heard of them before, even crapper, and it probably won't take nearly as much unluck for it to pan out poorly in the first place.)
If you have prime, just contact support. My experience is that it is a fairly fast painless process and they either just credit you right there, or allow you to free return the item for credit.
You should have left a seller review (on the seller's Amazon page), not a product review.