It is interesting how he bypass your "security" with OLD and out dated infos.
We all know who is responsible if someone used my coin without having current the coin password and email.
If you let all original owners who re-sell their coins to scam the amounts from the coins after selling them, believe me, not only your business is dead but your name in the bitcoin community.
No one than you can help the old owner to scam the value inside my coin.
https://bitcointalksearch.org/topic/solved-5093771
You resolved issue ? There was never issue, the OP is scammer who sold me the coin and then claimed this issue so he can steal the value inside the coin he sold me you stupid idiot.
Your security problems will cost you a bitcoin not me if you let him steal the coin value without him having the password and email of the coin in the very right time he sweep it. because I am the only one who have it and not the OP scammer.
Theres such a thing as a bitcoin blockchain that provides proof of transactions when you purchase something from somebody. Let's see your txid with a signed message from the address you paid from. Aswell, this is a perfect and prime example of why ESCROW should be used.
Edit to add: TitanBTC has many many loaded coins worth 10s of if not 100s of thousands of dollars in the hands of collectors. Their due diligence on something like this is a little more complex than you may think, theres a lot at stake if they make a mistake.