No doubt the nut has been replaced. Wonder what other work has been done to it? The bridge is clearly Asian spec, but it looks like it's been upgraded as well.
Will give the guy the benefit of the doubt, he bought a Chibson for $300 and then spent a few hundred getting work done on it - so he's just trying to get his money back. Not that I would spend close to $1,000 for a Chibson. And at least he is saying it's not real.
The two most important things to remember in life: "The only time it's acceptable to work with amateurs is if you are making porn." "If you want to work with clowns, join a circus."