Tell promising applicants the downside of the job as well as all of its potential and perks. Better yet, have someone who has actually done the job relate the frustrations and complications.
Reason: If you try to sugarcoat the position, your new hire will soon conclude you were either deceitful or ill-informed. If the disparity between what you describe and reality is great enough, that painstakingly screened and interviewed new hire may feel justified in looking elsewhere.
On the other hand, when you spell out the difficulties and possible frustrations, the person who accepts the job anyway will take great pride in meeting the challenge.