So I am attempting to gain rep for the Steel Songs. I’m running missions for them and after success there is either no positive change or my rep declines for them. Why would I lose rep for a successful faction mission? I don’t mean the opposing faction, I mean the one I’m working for.
It happened to me multiple times actually. In one playthrough I even lost 3 ranks, because they sent me against their allies. Another case where you can lose a lot of rep (and rep is the very reason why I don't do them) are assassination and capture contracts. I once took an assassination contract for Steel songs and encountered a chameleon - Steel song warship. As a spy without predator tracking array I had 2 options. To fail the contract or to lose a ton of rep by destroying the ship. I destroyed it of course. Net reputation gain? -12 points.
Interestingly enough, after this mission I took 3 more missions, passengers and cargo. Lost additional reputation, because I was carrying people operating in Steel song. So by doing contracts for Steel song I earned a criminal flag from them A further irony is, it was a steel song captain and ss were the only faction left to give me a rank.