When selling on Ebay you will make losses on some items that are you fault. Ebay has now added to that list some dubious claims that are not really your fault. These will frustrate you, but are probably small in total compared to losses due to your own error. So it mainly becomes a matter of principle.

My advise is accept you are going to make laooses and dont sell or ship anything that you can't afford to risk loosing. Much the same as a store has to accept a certain loss rate by having items on shelves rather than locked away.

Once you accept you will make losses, you will not get as stressed being defensive over who's fault issues are. I work on the principle if I make a mistake then I cover it, even if it could be argued both parties are at fault.

No point being here if its going to give you sleepless nights over a few dollars.