Let me begin with a dollop of brutal honesty. We understand next to nothing about psychopomps. Oh, entire bookcases have been filled with myth and conjecture. You could spend decades sorting through it all. At the end of that, you'll know just about as much of value as you will after reading this.
Definition
So what are we speaking of? In almost every mythological family, we can find stories of beings that guide the souls of the recently deceased towards their afterlife. There are a number of commonalities; Most often these beings resemble animals. Birds associated with death, such as crows, vultures, and owls are especially common. Other times they are personified as deities, such as Hermes, or even as incorporeal spirits themselves.
The most persevering trait is the psychopomp's function as a guide for the departed. They are not judges, nor tormentors. Their function is simply to guide. They show the way, and thereby allow the soul to go where it needs to. This is certainly in keeping with the ability to self-determine of most ghosts that I have come across, which they tend to be abysmal at.
Manifestation
Unlike the skill to perceive incorporeal beings, the ability to spot a psychopomp for what it is can be considered very rare. Even among the elders of la famiglia, few can determine their presence with any surety. Hence, I would advise you to keep a wary eye for animals that display unusual behaviour. A particular animal looking a bit ''off,'' is another sign.
The reason why so many of us prefer to work in crypts - apart from a preference for the dramatic - is that birds are rarely seen there, and have a tendency to stand out. So would a deity, presumably.
Accounts vary of psychopomps sometimes appearing in groups, or their reason for doing so. If they can even be said to possess the ability to have a reason for anything at all. Perhaps some individuals attract their attention to a greater degree, but why that might be I cannot fathom. I have seen no correlation between the presence of psychopomps and the social status, wealth, or emotional impact of the recently deceased.
Whether alone or in a group, psychopomps have never been known to interfere in any corporeal affair. I know of no reliable accounts that prove otherwise. They watch. They wait. Unnerving, but ultimately not bothersome. I am sure you can safely disregard any rumors regarding the disappearance of Necromancers who attempted to chase away or capture a psychopomp.
The frequency of their manifestations is an issue of great controversy. Some see them almost every single time they work, unless they work in a very isolated area. Others never notice them at all. I suspect that there might be many more variables than we are aware of, but I see little point in speculating about them here.
Conjecture
There are numerous theories that the absence of a psychopomp increases or guarantees the chance of a recently deceased person leaving a ghost behind. I am not aware of any truly conclusive experiment regarding this. Anecdotally, I can confirm that their very presence interferes with attempts to bind a ghost. Though the psychopomp appears to take no action, a ghost who perceives their presence will be motivated to move towards them with great haste. This can be prevented with the usual means, but it makes getting their attention that much more difficult.
Interestingly, it appears that psychopomps appear only for the recently deceased, if they appear at all. I have never noticed their presence near any ghost that wasn't very recently created, or heard of such a thing occurring from an uncle or auntie. I get the sense that a psychopomp is a one-time chance of sorts.
Attempts to follow psychopomps or somehow keep track them are almost inevitably fruitless. Few even try in modern nights. What is known, is that areas that have a strong connection to death see an increase in their presence. This suggests that they originate from the Great Below, perhaps ferrying their charges towards there and returning afterwards.
Conclusion
The existence of psychopomps is a secondary reason why we do not often attempt to create ghosts willfully, at least not outside of the family. The primary reason being, naturally, that this process has long since proven unreliable to begin with.
I would generally advise you to simply leave them be. Attempts to communicate with them are fruitless, attempts to interfere with them are foolish.