I think you're understating people's ability to listen to their own body, and using an ungenerous definition of 'feeling'.

Listening to your body is a skill that can be developed over time. Several years ago, I did not pay attention to, or was not aware of, any relation between what I ate, and how my body felt afterwards, what things looked like on the other end, etcetera. After starting to work out and taking my health seriously, I spent more time tracking things like 'how does food X agree with my stomach? How does it affect my energy levels when I have sugar in the morning?', and learned a lot. There are foods now I'm very hesitant to touch, that I would have eaten without a second thought several years ago, because I now know they affect me personally in undesirable ways.

This is not to say that one should eschew the scientific literature, or their doctor's advice. You should just take both into account.

To play devil's advocate, use of the placebo effect has always been considered morally justifiable in the medical field.

I think the context is in how the person feels physically and psychologically in the long-term. Psychics seem to market to those who have a short-term life issue like needing closure from a dead loved one or needing to know if their luck is going to change.

On the other hand, completely ignoring subjective comfort is also demonstrably absurd.

You can still tell them the truth. You can say "we don't know if the supplement is doing anything useful chemically, but the act of taking it seems to help you." I wouldn't have any trouble morally justifying that.

> By that metric, psychics saying they can talk to your loved ones can be morally justifiable.

A truly altruistic lie, while less moral to tell than the truth, can in many cases be more compassionate and do less harm over the long run.

Issue is, there are very few truly altruistic lies (most of them are told in obituaries, goes the pithy one-liner). Most seemingly-non-damaging lies are told for dual benefit if the liar and the recipient. In your example, the psychic is out to make a buck. This is personal and debatable, but I consider such "it makes you feel good but I'm only telling you 'cause it enriches me" statements to be less moral than truly altruistic lies (which are less moral than the truth), but more moral than malicious/victimizing lies (e.g. "no, Charlie Brown, I won't move the football this time").