UPDATE:
Basically he sent it two weeks ago with recorded postage, so it's Royal Mail's fault, he's planning on emailing me proof of postage tonight which we can hopefully get sorted out with RM.
The reason I was so suspicious was because he didn't responded to my message a week ago which asked whether he had sent it or not, making me believe I had been scammed.
Hopefully everything works out, but I've given up hope for ever seeing my keyboard again, knowing Royal Mail it's probably sitting down an alleyway in Sydney.