Thanks for the advice beach_and_home. Unfortunately I don't normally have time to check every buyer's feedback and in this case the buyer had 100% positive feedback - it's only when you view the feedback she's left for others that you get a true sense of what her transactions have been like. I normally try to accommodate a buyer's requests if I'm able to but I think in this case I was just unlucky to strike out with someone who's missing a few screws (if I can be frank). I actually do think the buyer has mental issues as her emails have been rambling to the point of disturbing. I made the mistake of giving her my mobile number to arrange the attempted pick ups and was concerned she might call me but she hasn't so far.
I'll definitely be reluctant to make similar arrangements with buyers in future. I think you're right, the postage cost and method were clearly specified in the listing from the beginning and I will stick to this in future. It was the buyer's changes of mind which delayed the whole process and led to this problem. Incidentally she lives in Leura and I'm in Sydney - she was planning to make the long trip on two occasions just to save a few dollars in postage but is suddenly put out because she couldn't get delivery within a week over Christmas? The logic applied by some buyers is truly bizarre.