How many people have had this happen?? It seems a lot more prevalent in the UK. Over here there's so little interest in anything megalithic that I doubt there's huge demand for anything apart from Newgrange, Poulnabrone and a handful of others. The market for those photos is probably awash already anyway. Maybe I'm wrong and there is a megalithic underground I'm not aware of...
The Irish Times, one of the 'big two' national papers have a big supplement today on Irelands heritage, it looked like they found a tourists disposable camera judging by the photos they chose for the supplement apart from one of Poulnabrone on the back page.
I would love to see my own photos on a wall rather than a brochure or some soul-less publication and probably will try to sell some once I get my monitor calibrated properly, maybe I'll change my attitude then!