The existence and common cause of dead spots is well known ... eg https://acoustics.org/pressroom/httpdocs/137th/fleischer.html If due to particular neck resonant frequencies, they are often un-fixable (although changing the mass properties of the neck may alter/reduce them). Some guitars are more subject to them than others. And savvy owners usually know the guitars that have bad ones, particularly if their playing relies on sustain. Which is often why they want to sell the guitars if they happen to be saddled with one. Particularly if they paid $3k for it. So while most people seem to be implicating the OP as the problem here, they ignore the possibility that the seller knows his guitar has one or more bad dead spots. Note that he said 'every guitar has some dead spot'. But he's obviously not going to sell to the OP anyway, so he's not going to admit that he knows his guitar has that issue.