Yes GM's should be able to sell some players on their teams, you aren't going to be able to do that with all players and that's also assuming the other team allows you to speak with them at all.
The fact is Buffalo is still seen as a basement team, but that's not the only issue. Rough winters and High NYS taxes are also working against them. Teams like the Rangers can attract players despite the high taxes because it's NYC, but even then the Rangers often end up overpaying some players to get them there. If you're Hertl with a full NMC who are you choosing? Buffalo or Vegas? That's not a difficult decision.
We know Adams was in on Chychrun, and there were rumors of Pesce as well but Pesce would not waive for Buffalo. Players have killed trades to Edmonton in the same manner, and that's a team with the best player in the world.
My point is, losing out on 1 or 2 players you wanted doesn't mean the Gm is failing, there are many variables and it's still early, there could be a big fish landed that we may not expect.