With classic bank transfer payment could be always reversed (even 30 days later). ok maybe for a banana this will not happens but it must be taking in account.
This is not true, reversing a bank transaction is not easy, you need to contact a bank and ask them to do so, and they will review your case manually. You only have a good chance of reversing a transaction if your money got stolen and you reacted swiftly. But banks generally rely of layers of verification to prevent that from happening.
Yes, reversing a bank transaction is not easy or even impossible if we don't have any concrete proof. There are a lot of wrong account transfers happening to people I know, and they can't get their money back because the bank requires too much proof, and it will take a lot of our time. Unless it is a large amount we should pursue it to the end, but if it is a small amount then we should forget about it.