I suspect Nigel might be the better one to answer - but I thought the Moar's job was fixed some years in advance so that the job cycled between the major landholders (I'm sure I've seen such lists) ; The setting quest I thought were selected on basis of rotation, availability + distribution between families from the major landholders - the coroner was a paid job but appointed (by governor) I thought on a per year basis tho could be held for successive years
Some brief quotes at www.manxnotebook.com/people/glossary.htm