Thanks for the replies everyone, it's clearly a lost cause and put me off ebay a bit.  I still don't think I did anything wrong.  I don't have any proof whatsoever that there was something wrong with the item. I don't actually believe there was.  I suspect he/she didn't actually want it anymore and that's why it took so long to pay.

I think it's very unfair to take 10 days to pay for something, and not respond to any messages about payment, then expect a response about a dispute in such a short time. I've also just checked the reciept from the post office, and it was nearly another 10 days that he/she sent me a message about the item - although I can't be sure when the item actually arrived to the buyer - but I don't think they had the item much less than a week before they sent me that message.  Giving me even more reason to believe they just didn't want it anymore.

Also, if she send me a message on Sat and neg's me on Mon, I consider that to be 2 days, not 3, only 48 hours have passed.  By the time I saw it on Tue morning, not even 3 days have passed.  And, only 1 business day -  even ebay gives people 3 business days to respond to disputes.

When I do have listiings and waiting on payments I do log in daily, but I when I don't have listings and it's been so long since I sent items, I don't see the need to log in as often.

Anyway, I clearly just have to try and get over it.