I'd then turn this back to them as a warranty case - I have standoffs and the cable in my box, but it was a pre-release one, so I wasn't 100% sure. Now I see Mouser lists the same set, so I think we are safe to assume that's a standard retail set. You should also have a paper Quick Start Guide in the box (like that), which mentions the USB cable, it could help you prove you're right if the seller has any doubts about that.
Oh, and there's also Intel Support link you could try if for whatever reason it doesn't work out with the seller.
Message was edited by: AlexT_Intel: Added link to Intel Galileo Support