A lot of threads have been created about how to avoid scams on exchange p2p especially the area of making sure you have confirmed the exact amount sent to you before releasing your crypto asset. In the case of your experience, it could be that the vendor sent the transaction and later reported it as a dispute transaction that is why it showed as failed from your end. What i literally do whenever i receive money from any p2p vendor is to transfer the funds to my other bank account so that there will be no case of reversing the transaction by the sender but some people when they just get a notification from their banking app they will immediately release crypto just because they want to be fast with the transaction but it is always good to confirm payments by opening your banking app and see if it is also added to the existing balance you have initially before you release crypto to the merchant.