Ok i've had this problem with my 3rd string for quite some time. The intonation is off, and it almost always sounds sharp. I've moved the string saddle back and its helped somewhat. When I tune it to a perfect G it sounds good. When I fret it up the neck (fret 5 and up) it sounds ok, but if i fret it low (< fret 5) it sounds sharp.

So I went to my local music shop and asked someone there, and he says it could be the nut. He says if I file the nut, just for the 3rd string it could help.

Is he right? If so, how do I file the nut?

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