"The worth of an item can only be measured in the hands of the person holding it"
That's the value of the item based on one individuals perception of its worth, NOT fair market value, which is based on a cross-section of the buying public with a specific interest in the item.
The two are very different, let’s not get confused.
Having said all that how did the gentleman arrive at the $100 value for the TT? Is it the buyer who has responsibility for researching fair market value, or the seller? (obviously the seller). Is old age a good reason not to be able to research fair market value, in this instance, no, sorry it isn't. The gentleman was 'aware' enough to be able to make the necessary arrangements to place the advertisement, and would surely have taken one step further to research the items value, had he been so inclined. Maybe the old guy stole it and thought $100 for hot merchandise was a good deal. Who knows what circumstances were in play.
As for the little Picasso story, cute, but a poor analogy for what is going on here.
pW