That's not relevant here, it doesn't affect the customer service; what does 'actually came from them' mean in the context of who is the seller in the transaction?

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.)