Restore My Sister's iPhone: Frauded by eBay Seller

Hello everyone, I'm a college student from Northern California. Recently, for my younger sister's birthday, I forked up enough money to buy her an excellent condition iPhone 13 Pro Max, as I love her and she means the world to me for all she has done. In the end, it cost around half a grand. Unfortunately, the seller did NOT state or notify me of any display damages prior to selling me this phone as the screen looks physically "new" with no scratches but is now stuck on a yellow screen that has apparently affected other users as well with the same model. It worked perfectly fine for not even a day before issues arose, and he would not accept returns. Even after I contacted eBay support for the money-back guarantee policy, I still had no luck. I even attempted to fix it myself by opening up the phone, but nothing has budged.

Fortunately, the entire phone does not need to be replaced, just the screen, which is still fairly costly and I don't have that kind of money to fork up again right now. I'm disappointed and upset my sister has to deal with this as she has told me many times her current phone has been having many issues. Any donations, little or big, would mean the world to both of us. Thank you for your kind consideration, I will try to update you all with photos of the new screen in action, God bless!