This term refers to being the victim of someone who has deliberately and intentionally swindled, grifted or in any manner taken advantage of, always in an unfair manner.

Someone who has schiested you has fucked you out of something.

People who've been schiested not only live with the loss of money or property but also the disappointment of having let themselves be taken advantage of. As such, many people who get schiested never report the incident due to the loss of pride and self respect, making it one of the most underrated problems in modern society.