I have read all this with interest and there is one point I would like to home in on, and that is the question of return postage.
If I have a complaint about a purchase, I always go to 'Other' to contact them first, send a polite but firm message saying the item is not as described and would like a refund. I then go on to say that if the seller would like it returned, then I am very happy to do so, but only at the sellers cost as it is not my fault that the item needs to be returned.
I always use the eBay message system and if they reply by email, I copy and paste their email reply into the eBay message system, saying I will only correspond this way and that I hope they will be honourable enough to refund me within the next 8 days.
This usually elicits a refund, most don't want a return, those that do will need to either put the money in my PayPal account before I will post it, and remind them I am sending it 'Signed For'. Otherwise they will have to escalate the case themselves, in which case, eBay have access to all the correspondence and will see I have said I will return it at their cost.
To date, have never had a problem, the two items that were returned were both return postage paid by the seller.
The message here really is 'Clear Communication'...
Tell the seller what is wrong
Ask what he will do about it.
Offer to return at their cost.
Only open a case as a last resort.
If they refund and pay return postage, I always leave positive feedback, even if only to say 'Transaction completed satisfactorily.'