Any chance that each seller could have a message board that had a button to it on each auction. Something that sellers could put a message on like "I will be away from xxxx to xxxx and unable to send items or respond to messages during this time" or "I have been unwell and unable to send items - all items will be sent by xxxx".
Just an idea so that if a seller had a problem or a holiday or anything else like that, the seller could check the auction and see if there is a message as to why they haven't received goods or had a response.
There could be a button that automatically got added to every auction that linked to the message so that if there WAS a problem or a holiday coming up you only had to change the message on that board, not every auction.
I hope this makes sense!