Speaker purchase question

Technically, the seller is right, however,  he/she is NOT an upfront or transparent seller.  I would’ve been majorly disappointed, both in the purchase, and with the seller.  Sellers have a responsibility to be accurate and also clear, and my gut is this was a premeditated omission. 

You can leave feedback that is fair and honest, while not being negative. I think the seller deserves feedback that encourages other buyers to inquire carefully before purchasing anything from him/her. 
Personally, I think you have a responsibility to leave feedback like this. A community like ours needs accountability, which you can achieve without being nasty.

If the seller is lurking on this post, I hope you realize you still have a chance to make this right.

reading all these replies, i do wonder... what was the seller feedback rating on a-gon?  good?  extensive?  

that aspect can be telling, and to me, it is a bellweather as to the level of attention i pay when considering a used item to purchase

'Caveat Emptor'... buyer beware. 
'Caveat Venditor' let the seller beware is a modern version.

If the speakers were sold "As Is"  then he was selling what you see in the photo with no implied warranty. It is what it is.

If NOT sold  'As is'  he clearly created an 'omission of detail' that lessens the value of the represented product. It's not unreasonable to believe the speakers would come complete unless he otherwise stated such. If this is the case, then he should at least be called out for his deceptive intent and warn the community.

Definitely seller fault so far as he didn’t mention on ad or description 
if he’s not willing to negotiate the replacement price then contact PayPal or your credit card 💳 company to return it so next time he’s going to learn 

"Am I wrong to feel deceived?"

Morally, most likely, no. Legally, based on information here and without seeing the original ad, yes. The default position of any used item being sold is "As Is" regardless of that being said in the ad or not.

https://en.wikipedia.org/wiki/As_is

If a buyer makes assumptions about the item being sold, he is also assuming responsibility as well should he happen to be wrong.

Some sellers will tell everything even down to the most insignificant detail. Whether it is intentional or just their nature, other sellers will say very little. Nevertheless a seller is only wrong legally if he lies or gives misleading information.