One quick wy to check a guitars intonation (how 'in tune' it stays from fret to fret) is to ring the 12th fret harmonic on one string, then play that string fretted at the 12th fret...

If yer lucky, those 2 notes will ring exactly the same note...

More than likely one will be slightly (and we're hopefully only talking a few cents here) sharper than the other...

If you think it's out, when it doubt, ask a trained professional...

Oh Riiiiiiiiiick???

;-)