you are sorta right
the league page show me which players are available for sale in my league
tactically, from a game/season perspective, knowing that an opponent is selling in, perhaps an attempt to upgrade before seasons end, is tactically good information.
Now your right - knowing that that team is selling means you get first dibs on him. But everything from there on in is a normal purchase and will go through the normal purchase scrutiny.
buying a player for too much/too little etc.
so whilst the information on the league screen does give you notice that someone in your league is selling a player, and that does enable you to bid on him first, everything after is the same as me finding a player on the transfer market.