Was it clear to eBay that the product was counterfeit?
In my case, when nettcy168 asked me to return the item to a USA address (which was strange), I replied that returning a counterfeit item was against eBay policy, and then nettcy168 refunded me quickly.
eBay is not able to say/tell if the item is counterfeit.
Even we don't know for "sure" if it is. Of course it actually is, but there is no official memo from Agilent stating that all genuine units have metal inner shielding / high quality soldering / etc.
What is most likely to happen is that if you contact eBay and tell them that the item is counterfeit and then the seller says it's not, eBay is going to tell you to return the item for a refund as they do not know if it is or it is not. The seller probably chose to refund you directly as they did not want to draw attention to themselves which throughout time could get them banned from eBay.
Also, many Chinese sellers have/partner with warehouses in the USA. It might also have been the case that the seller was actually trying to see if you really have no use for the item and would rather keep it rather than not have it and get your money back(this has happened to me where just before shipping out the item the seller said to keep it).