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How does PayPal decide based on what criteria? How can I fulfill these?

In terms of buyer protection for SEing purposes, here's how It generally works.

If something goes wrong with the purchase such as "the package did not arrive" or a "different Item was received", PayPal will try and correct It. Both of those quoted terms are listed on their website as "INR" (Item Not Received) and "SNAD" (Significantly Not As Described) - which Is equivalent to the DNA, (sometimes) the missing Item method and the wrong Item received method respectively.

Aside from unauthorized transactions, when putting In a dispute/claim, they're the only things you can use to get a refund - the "INR" (DNA, missing Item) or the "SNAD" (wrong Item received).