Alears said:
I wouldn't worry about the seller being amenable.
All very well in theory but what happens if the seller refuses? The Ebay/Paypal dispute process will require that the speakers are returned by a trackable courier, so rocking up on the seller's doorstep won't cut it. Ignoring the cost of shipping a pair of RS6s (always assuming the boxes are available), then all the seller has to do is refuse the delivery. Better to do it amicably rather than go in all guns blazing with threats.
Items that are collected & paid for in cash are in a bit of of a grey area as far as the dispute process is concerned, as there is no evidence that the transaction took place at all.
Looking at it from the seller's perspective, if the speakers were working & he's now landed with a pair with blown tweeters, he's likely to think that the OP has damaged them. The OP should really have requested a demo before parting with the cash but that's easily said in hindsight.