There is no way, on this planet that that money actually ends up in your account!!!!!
As Esav said, you need to contact a postal inspector.
Paypal, or USPS money order only. I don't send the knife until I literally have the cash from that postal money order in my wallet, and am walking out.
Ive had a local postal guy tell me a big money order was fraudulent. He would not cash until he had another worker check it. It was real, and I had my cash, but if it had been fake? No big deal, I had not sent anything yet.
If a buyer has no feed back? I have asked for USPS money order or nothing! (No pay pal from some one with absolutely no feed back).
He tried to get me to ship without me receiving the money order. I did not. I eventually got that money order (two weeks after he insisted I must have received it, then that his girl friend had sent it, then, oops, she told me she sent it but did not).
I simply don't need to sell a knife bad enough to risk it, and if it costs me a sale, fine, some one else will come along. I am the seller, and my rules are what control my sales.
I don't have a lot of feed back on here. Ive done my share of deals, and I have never been scammed, but I'm careful.
I would suggest the money is not going to clear. If you refund him, you will be out your knives, and out your money if you try to refund.
Even if the cashiers check turns out to be real, you are still going to have this guy trying to get money back for knives received.
This buyer, with less than a month, and no posts besides to steal your knives, has absolutely nothing to loose by burning a throw away account on here.