Can’t believe some of the comments. Seller advertised working speakers. You received non-working speakers. I’m skeptical like many others that shipping caused both tweeters to fail. But it doesn’t matter, shipping damage is the seller’s problem, not yours. You paid to receive working speakers, as advertised.
Seller should have paid for return shipping, ordered new tweeters, had them installed himself, and put the speakers up for sale again, with the ad stating tweeters had been replaced.
By offering only to pay for new tweeters, the seller did not take into consideration your extended wait time to receive new tweeters, the possibility that more extensive repairs are needed if the new tweeters fail, and your time and effort to do the repairs yourself. For all that hassle, you are owed a partial refund. So, seller should have give you two options - return broken speakers for a full refund or a negotiated partial refund for your time, effort and risk in taking on the repair of the speakers yourself.
If I were you, I would be pissed and pursue an acceptable remedy, because as things stand the seller has ripped you off.