I do not think that ghosts are, because they have left the world of the material and have moved into the world of the spiritual, and then from then on they just haunt and annoy those that can sense them… not everyone can.
The ancient celts believed they could pay off debts in the otherworld, and according to the romans they would use that idea. To them the otherworld, is literally another world/s, and the beings which dwell there are people. I don’t think they would refer to themselves as the dead or some such thing. A ghost I would imagine is like some cosmic recording or echo of e.g. a traumatic event, which somehow left its imprint upon the fabric of time. I got no way to substantiate that of course.
financial ones were what I heard mentioned. I expect ancient Britons had every conceivable way to pay debts one could think of, and more ways than we even want think about lol.