In eBay's defense because of their policies there is not much they can do 45 days after the sale, this is to give some protection to the sellers, before that the buyer has all the power, if an item is new or used the buyer has 45 days to open a case no matter what the seller states, the 30 day "return" window is for returning an item that does not fit (the buyer has some responsibility to make sure the item they buy is the correct item but in automotive parts if you use the part locator you are covered) or the buyer just does not want the item (buyers remorse) and the buyer usually has to pay return shipping and possibly a restocking fee.
I have bought literally 10s of thousands of items off of eBay since joining in 1998 and have returned my share of items, I have never had a return case for a defective item not go my way, I have also sold hundreds of items on eBay (mostly refurbished Motorola two way radios) and for the most part have not had many issues, I did have one case that stands out, the seller falsely stated the radio did not work then just tossed the radio in the same box I shipped it in only without any packing material and it was pretty beat up when I got it back, I had to take that one on the chin.
However eBay telling you to return the items without getting authorization from the seller was wrong, especially after 45 days as they do not have that authority.
One thing has changed in recent years, it used to be if the seller sold an item as "used" it had to work, if you clicked on the item condition in the sale it would drop a window that stated something like "the item is used but fully functional" so ALL items sold as used must be working, only items sold with the condition "for parts only" were exempt, but now if you click on the condition and if sold as used it can say see sellers description, I have not had any issues with those so I cannot say how a case would go, I am confident if the description says it is working then you would be covered,
It used to be if sold used it mattered not what the description said it had to work.