I' m guessing that if an instrument is sold with a guarantee from the seller that said instrument is exactly what its meant to be , then there must be some legal recourse if the instrument turns out to be a fake . I wonder how often sellers are actually under the impression that they 'may' be selling fakes ? If I had the funds to go and buy an antique Italian Masterpiece then I'd be sure to have it carbon dated just in case it may be 'off' by 100 years or so
I also suppose that if a dealer knowingly sold you a fake instrument you may be able to lay a charge of fraud , whether or not you could prove that the seller actually was aware that he was selling a fake is another thing......