How would you suggest going about buying used enterprise gear? I was thrilled to get a decommissioned optiplex and old monitor from an old job, but that's just

How would you suggest going about buying used enterprise gear? I was thrilled to get a decommissioned optiplex and old monitor from an old job, but that's just because I happened to be in the office the day the stuff was lying around. Otherwise I have no idea how to get that kind of stuff