He sends the btc to a localbtc address. There is no way that you know that the address he sends to is a localbtc address.
There are ways to find it out. Most of the localbitcoins wallets are tagged. Even if they are not, we can send alerts to the localbitcoins admins.
If I had some btc laying around, I would prove to you that you cannot trace coins for longer than 24 hours, if someone does not want you to. This guy is just a moron.
Care to place a bet? Have someone send me .01 btc, and then tag it however you want. I bet you wont be able to trace it, and I will return it totally clean, no tumbler service needed.