What should I do...

So as stated before I am in a dispute on paypal and the buyer is trying to send me back a product that has been used this claim has been going on for a month now.. He paypal told him to send the item back and it is suppose to be delivered today so if I reject the item when it gets to my door then what happens ?

Well the buyer put the wrong tracking number on the case, the product said it was delivered last week.. The buyer emailed me giving me the new number saying they was going to give it to paypal... I went to paypal resolution center today and it went from "item returned" to "being reviewed by paypal" which is backwards.. And I do not see any tracking number in the case so i don't know what happened... And how can I win...