Seller being difficult about returns

[yugiohcards4]

So I recently purchased some YuGiOh cards from someone on eBay (I predominantly buy and sell YuGiOh's so I kinda know what I'm looking at/looking for) and  today I recieved those cards and most of them (about 90%) are fake cards. I have opened a case with eBay and PayPal on the returns front but I am curious as to what will happen if they claim not everything was sent back? 

I bought approxiamately 2000 cards from this guy and he's been constantly accusing me of taking out cards (even before I've returned the item) even though I haven't and I was just wondering how it would affect the case if he throws in a formal accusation of this happening. Again I have left all the cards in the packaging that I recieved them in and will be returning them in that package but I just want some advice on this issue. 

I buy and sell so I know how tricky customers can be (never really met a difficult seller though)

Thanks!

[ruby*tuesday · Accepted solution]

The Seller would have to Appeal Ebay's decision to Refund you, claiming some Cards are Missing. As long as you use the EBay Returns Label which shows as Delivered to the Seller, there is little chance of EBay Reversing the Decision.