I think he's taken the one injector he needed and is now looking for a full refund! Unfortunately there's people who do this quite regularly.
Oddly enough, I've just had the exact opposite of this.
Bought 3 injectors and inlet manifold off the bay.
It arrived, 1 of the 3 injectors is broken. (luckily I only actually needed 1, and the other was for a mate, the 3rd was going to be a spare)
I checked all the packaging, it could very well have been a genuine error, or the courier could have done their usual.
I messaged the seller, and his response was,
'Yea, it was probably damaged before I sent it, I didn't bother checking.
you got 2 injectors and a manifold delivered for £30, so what's your problem, that's a proper bargain'