Its stupid really,  a simple function would be to have a "holiday mode", ebay has it.  Where all listing are simply "not visable" to buyers for the period your away.   Editing my 450 lisitngs individually is not something I have time for, if you deactivate and let them time out in the days before, thats a good deal of lost sales and starting it all up again is a pain, redoing stock levels etc.

A little patience required on the buyers part by the looks. These things happen.  

Providing the seller gives a 100% refund,  I see no reason why they cannot back out of a sale. I have done this, for the same reason as Callum,  however in my case the buyer got very abusive, threatening me with the police etc. My mistake was also very obvious, a $950 item offered for $9.50