There are far more uninformed buyers than there are ones like those that frequent this board.  I also agree with Walt, we are not the keepers of the values, or we could still buy pristine high grade Parkers, Elsies, Ithacas and LeFevers for under 500 bucks.  That is until we want to sell them..... then the figures increase exponentially........ Go figure.....
As far as i am concerned if that seller can get six grand for that gun, more power to her.
As far as selling "Worthless Treatments" is concerned, it is not fraud to order x-rays, imagaging, lab work, etc, etc all with many thousands of dollars in billing while sending the referrals  through labs and companies that the Doctor has a controlling interest in, only to find out you only have a common cold. This "practice" I believe is more common than I even want to speculate on.
Caveat Emptor still prevails, guns, cars or doctors