Good luck to the buyer ... having to keep his fingers crossed you didn't keep a copy of the backup.
While this may very well be a legit request, I would definitely strongly advice people against buying wallet backup files from others. There's absolutely no way to tell if you get scammed by someone claiming to have uninstalled and deleted the backup after they sent it to you - but turn out not to.
As the saying goes for all crypto: With full control comes full responsibility. If people get cheated, scammed, hacked or looses their funds, there's nobody that can help.
RE: I NEED HELP! Can I sell my Byteball Wallet? [Best Discount Price]