Speaker purchase question

I have been a member here for 22 years, but encountered something today for the first time and would appreciate your opinions. 
I bought a pair of used speakers on Agon and they arrived with no grilles. The seller is stating that the pics did not have grilles (true) and they were not mentioned in the ad. These Rega speakers did come standard with grilles originally. I thought that the pics were taken to show the condition of the drivers. When I asked the seller, he said that he had looked into buying new grilles, but since he didn't mention them in the ad, it should have been obvious they weren't included. 
Am I wrong to feel deceived? I want to be reasonable and would be interested to hear other opinions. 

In what condition were the speakers rated?
Missing parts should drop the rating, wrong assumption from your side.

“Btw, did the ad say that only what is pictured is included? If not then it's his fault again”

No, this was not stated.
IMO, best practice: anything that was originally included by manufacturer and is not present at resale should be explicitly mentioned.

That said, the grills were not pictured, and seller did not actively mislead, so he's got a case; I doubt what happened rises to the level of fraudulent misrepresentation.
(A friend of mine one sold a very old BMW 5 series, and the frame broke the next day.  In small claims court, the judge ruled that to get relief, the buyer would have to show that he was *prevented* from inspecting the frame.)

Perhaps a fair solution would be for seller to offer some consideration towards new grills (50%?), so everybody could walk away feeling reasonably whole.
I'm optimistic about  such a concession, though, esp. since the cost of replacement grills might be extortionate,