That's pretty much what he's paid to do. Only problem, from his perspective or his clients' perspective, is if his reputation is so bad that teams won't deal with him, but that isn't going to happen with quality players.
If quality players end up taking less because of strong-arming, refusal to work with teams, etc.?
Absolutely, it will.
I don't understand where people think reputations, business negotiations, and how you represent yourself (and your clients!) in these discussions don't have lasting impacts.
Everybody wants their team to win every trade - problem is, if you start doing that, nobody trades with you at some point. It's why GMs are so gun shy now and would rather just stand pat and pray.
Do star players hold teams over the barrel? Absolutely. Do teams do so with star players? Absolutely. You can do it sometimes; and win. You do it all the time, and you lose.
As an agent, you can represent your client's interests professionally - without stepping over the line. If CG wants to be traded, ok? Work it out with the team, and get him traded. Don't go silent treatment like a petulant child, and don't advise your client to do so.
In the NHL, Zeev Buium falling a few spots isn't a big deal - in other sports, and maybe in the next CBA, draft position may affect your compensation - is it worth it then?
Leaking Trouba may not report does what now? The team wants to move him - and he doesn't want to go. There's still 20 teams he can be traded to, why not behave the same way out of spite and move him to the worst of those 20? The team can respond that way - luckily, they are usually more professional. Also, now it's public knowledge and it doesn't benefit the team or the player. And if NYR responds by just scratching him indefinitely? Is that a better solution?
Teams are sometimes stupid, but they do care about maintaining some semblance of image (most do, anyway). But an agent's job is to represent the actions of his client (often very young clients) and educate them how to be professionals. I don't blame the players here. This agent behaves like his very immature clients.