There are at least witnesses who saw the box of treasure before he supposedly hid it. Â (He kept it for a few years after his cancer went into remission.) Â Also, he donates all proceeds from the book with the clues. Â And everyone who knows him says that, yes, this is exactly the sort of melodramatic stunt he’d pull. Â For instance, Fenn also casts bronze bells with messages to ring it for him if found, and buries them all over the American west. Â He likes the idea of being remembered (which admittedly a hoax would also accomplish) but the treasure supposedly includes a copy of his memoirs. Â He’s an eccentric guy. Â He also seems semi-responsible about it: for instance when people started digging up old graves he specified that it is not in a grave, and when people got in trouble by breaking into bathrooms in national parks he specified that “warm waters halt” has nothing to do with a bathroom, etc.
The big issue of course is if someone who finds it can even legally claim it. Â If it’s on public land it’s almost certainly illegal to remove it (it would be an artifact), and if it’s on private land it belongs to the property owner. Â There are legal arguments to be made, of course- for instance that the treasure wasn’t “abandoned” in a legal sense, but rather left for whomever finds it, etc. Â And believe it or not there is a legal definition of “treasure”, and it does imply “finders keepers” to a certain extent, depending upon the state. Â Nonetheless, the best option for whomever finds may be to never ever say where they found it…
I included checking out a Fenn solve on our trip to Yellowstone last year. Â If nothing else, it gives you ideas of where to hike:

In retrospect it wasn’t a good solve- there’s no way an 80-year-old could have hiked to it from his car twice in one day (which is another clue he has given).
Even if it is a hoax I think it’s a great idea to get more people outdoors. Â Not to mention that it’s just FUN, dammit! Â But I guess I don’t think it is a hoax.