Which is why I said 'or at least claimed to be'. However, I have also met various ex-patients since I left that job, at a point where that power relationship was almost completely gone (of course there might be residues of it, but I had no actual power over them) and they've volunteered the same information. Also, I have several friends with psychiatric problems who've said the same kind of thing about their own experiences, and who haven't ever been patients anywhere where I've worked.
(Also, in my experience, patients trusted me with confidences with which they didn't trust the other staff members - I was better at building up trust relationships with patients than most staff were).
On the whole I think that even allowing for the strong motivation to lie, I think that a minimum of 75% of those who said they were grateful actually were grateful. And while I am in principle in favour of people being allowed to kill themselves, I think saving the lives of three people whose (if you like) CEV is actually that they don't want to be dead is worth the temporary inconvenience to the fourth who really does want to be dead and who is not mentally ill. (I actually think the numbers are skewed far more towards those who don't really want to die).
People in that situation would have every reason to lie to you, though, wouldn't they?