To answer a few questions.
Although an altered Mantle does hold some value (and if it's a PSA 8 Wagner a lot of value
), it was not the consideration that the seller initially offered the buyer. Since the seller maintained that the card was in "near mint condition" the card must present as such or a breach has occurred. Additionally since the seller was considered an "expert" and the buyer someone unfamiliar with the industry the court gave the buyer the benefit of the doubt.
Savedfrommyspokes makes a valid defense argument, but unfortunately the defendant agreed that the card was the same card sold and instead sought a sort of "silence is acceptance" style defense. I too find the courts decision a little too favorable to the plaintiff. If the case occurred today, I think the courts decision would likely swing the other way. Far too many authenticators and graders to raise the "I didn't know" argument.