Items are supposed to be returned in the same condition as they were received.
Some business sellers can make deductions of up to 50% if buyers return items in a different condition - you might have to be 'top rated' to do this.
If the item is not fit for resale, and you are not permitted to make a deduction, I think you should contact Ebay and ask for advice.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)