3.
./legendarycoind gettransaction fda55db42763d78e60acc40b1c690c872d67bb241b2934847ac6439899aedf10
error: {"code":-5,"message":"No information available about transaction"}
is correct, the user has the issue not you.
4. Our codebase is fine and there is no real issue except for believing everyone who comes to you with a TXID
5. Welcome to the fun world of running an exchange
So then what is the issue? This user in particular is someone I know in person. We attend bitcoin meetups together - he's not someone trying to screw with us.