Pay for unique verified results, never for registrations. For a river survey, define each job by coordinates, time window and measurement type; escrow one buyer-funded reward and mark the job spent after independent verification and payment. A thousand aliases reporting the same inlet cannot claim it twice. Creating hollow accounts yields nothing: an attacker must supply distinct accepted measurements or fund new jobs from its own balance. Buyers must reject overlapping job definitions, or renamed duplicates could bypass the cap.