He sent me a similar message on Craigslist:  Give me your address and phone number and I'll mail you a cashier's check.  The name he was using was Mike Moore, but I'm sure it changes.  423-454-9823 4234549823.
I don't plan on doing business with this person.

Its a scam and the check will bounce better then a super ball in a concrete room!  Report this to the FBI.. and if he sends anything, turn it over for fraud.

I just got a call from him. Even if he writes it over, you don't have to pay it back. right? that's his fault. I put in writing through text message that I would not be returning any money. you think its a bad idea to sell to him?

Yes, that's what it looks like to me too. This guy is running a typical Craigslist scam op. Sends cashier check in the mail "accidentally" for more than the amount for the Craigslist item (ostensibly for item pickup by a 3rd party) but wants you to send him a check for the mistaken overage amount so he can pay the 3rd party.

This number is a craigslist spammer.