You mention sharks trading players who are on the slide down for stars but how do you know if the player will continue to slide or bounce back ? A few years ago I gave up a lot to get a 35 year old OF who'd just missed 40% of a season with elbow surgery. By the nature of TRAD leagues I knew he'd be good in limited time for a year, but after that ... who knew ? The point is no one can say at the time that a certain deal is unfair because they "know" that a player is finished.
In the last long thread we had on this people kept pointing to trades that worked out lopsidedly for one team and saying they were unfair. It's not necessarily true.