Guitars are worth what people are willing to pay. Any decent vintage electric for 150 isn't a bad deal, unless the guitar is unplayable. A busted nut, as you say, is one of the simplest repairs any guitar would need. If the guy isn't representing it falsely, how in the world can you have the nerve to say he is ripping people off? Did he sell it to numerous people? No. Did he say it was something other than what it is? We don't know, because you didn't cite any ad or article.

Mansfield guitar were decent instruments imported to Canada from Japan in the 60's and 70's.

Know what you are talking about before you spout something like that.

One last thought: Japanese guitars from the 60's were usually pretty crappy eclectic instruments, and didn't sound or play real well. But those are exactly what some artists look for for certain recordings today.