Of course it is their responsibility to take it back.
Suppose I order a watering can from the garden supply store. When I get home from work, I discover that instead of a watering can, they've delivered 2 tons of mulch in a giant pile in my driveway.
I'm not sure how you could make the argument that it's now my responsibility to get rid of the mulch that I didn't want or ask for?
I agree, but the argument is also bullshit. You've changed the [noun] specifically to create an example where disposal is onerous. If disposal is not onerous, it looks quite a bit different. Are we so inflexible in our thought that we require a strict rule to be applied all cases, without the bit of common sense that says: "If you created a massive burden on me, it's your responsibility. If you created a negligible burden on me, who gives a shit?"
If they delivered, instead of two tons of mulch, a single unit of scotch tape, would you still give a shit about whose responsibility disposal is?
We can go ahead and treat these cases as distinct, because they're distinct. You recognize that implicitly, which is why you made your example two tons of mulch, and not 2 ounces of plastic.
The customer will sadly always have to do something about an error... it's sad, but it's now in your property, there's a minimum of effort you'll need to do in every case.
Bare minimum effort:
1. Contact Amazon
2. a. Giving it back to a shipping carrier
b. Dispose of it
In the case of a server mother board, both giving it back to a shipping carrier and disposing of it is essentially the same effort (I would argue that giving it back to the shipping carrier will be more effort actually, but it's not worth the effort to argue that, so I'll say it's equivalent). That means complaining over it is petty.
In the case of "2 tons of mulch", or by definition anything "bulky to store, impossible to sell and costly to dispose of", the amount of effort isn't the same at all between disposing of it and letting a shipping carrier dealing with it. This make it complaining about it, not something petty.
Suppose I order a watering can from the garden supply store. When I get home from work, I discover that instead of a watering can, they've delivered 2 tons of mulch in a giant pile in my driveway.
I'm not sure how you could make the argument that it's now my responsibility to get rid of the mulch that I didn't want or ask for?