Spiritualism is a movement, a registered religion and also a philosophy that can help us cope with life's difficult times, especially during bereavement when we're often at our lowest.
Just as in this world, though, it's prudent to know whose words we're hearing and why we might heed them or ignore them.
The voices of spirits do not all have equal authoritativeness. Just as in this world some will have more understanding than others. Some may have little more spiritual understanding than the incarnates who listen to them. Not the ideal person to be paying much heed to.....
Just being 'dead' does not automatically convey omiscience - any more than being alive does.