You are correct, applealing against an ebay decision is very much a wate of time.
If you do not refund willingly, then you end up with a defect and no refund of seller fees.
Ebay never sees what is sent or received, so it is virtually impossible to prove your case. Far better would be to have a proper returns policy, where buyer has to pay for return postage for change of mind returns, instead of buyers inventing reasons where YOU have to pay for return postage,