That's the excuse/reason I have been given recently - only time I've ever had a problem too. Mind you this seller is no longer selling anything having had mainly excellent feedback on over 10000 transactions......
I've had the exact same situation as wowfudge (except my seller hadn't sold that much). What made me was that they had given me feedback but hadn't sent the item and when I looked at what others had left as feedback for them they had explained that they had just got out of hospital. So you could leave me feedback but not post? However like with wowfudge my seller is no longer selling anything and has closed their ebay shop down.
"they had explained that they had just got out of hospital. So you could leave me feedback but not post? "
Actually that part makes a lot of sense to me. You can get WiFi in hospital but you can't wrap & send your stuff. Once out of hospital, then must work thru a backlog to verify people really paid, then to carefully package & label, sending out the oldest stuff first assuming people haven't filed & won a case or asked to cancel. Then you have to arrange a courier or get to a courier depot. All when you're probably still feeling ill & the rest of your life has a huge backlog to deal with.
But they may be making it all up... I don't know either.
I think if you are up front and admit you have made a balls up most buyers are OK and understand we are all human and I've yet to meet Mr/Mrs Perfect,its the far better to say you forgot to post surely. Yesterday I did an early post of items I sold on Tuesday night and am now hoping I have put the right addresses on the right parcels,so I have e-mailed the buyers and told them I may have had a blonde moment and they are both fine.I am sure I have addressed them correctly but it saves from buyers going straight to INAD if one lady gets shoes and the other one gets boots.(God I hope I stuck the correct labels on)