The case of art appraisers mistakenly identifying a piece of art work found in a barn indicates a lack of skill on their part. It can be argued that the same mistake in the medical field could lead to a serious mis-diagnosis. If art appraisers can not decipher the difference between a famous work and that of a amateur then a serious re-evaluation needs to be made.
Art is incredibly subjective. What one person may see as a masterpiece, another may see as junk. Art appraisers generally know what they're doing because they've received training. They know the history of art and often specialize in a specific type or two. However, this doesn't mean they're incapable of error. The incident on the Antiques Road Show was unfortunate and one would hope more time is taken in the future to avoid such errors.
While an art appraiser mistakenly identified a 1970's school project as a 19th century piece, this is only one isolated incident. The person has accurately appraised countless pieces throughout their career. There are countless appraisers who identify artifacts accurately daily. Even highly educated professionals make mistakes. One error does not represent an entire industry, or the professional who made the error.
Yes, art appraisers know what they are doing, but they sometimes make mistakes. Just because they appraised this one ceramic jug incorrectly does not mean that they are all frauds. Maybe there was a similar look to this jug that much older jugs also had. It could have been an honest mistake.