If he said it "plays well" that's a direct representation about its playability, not about the electronics working. If he now says he was only referring to the electronics, that's bogus.
More important, if he failed to mention in the auction that there was very severe fret wear and it turns out that nine frets have grooves worn right down to the fingerboard, then it sure looks like he intended to deceive.
I'd insist he pay for repairs, whatever the cost, or take it back at his expense.