How to get the "Wheeling and Dealing" achievement and the "Master Negotiator" achievement:
Just start a career with a random team. Put 5+ players available for other teams to buy.
Also make 2 offers on other players and add one of your own players to the offer.
Advance and once you get a message for an offer made by another team make a counter offeer which is slightly higher than the offer which you received. This should get you the Master Negotiator achievement. Once you get a message that your offer has been accepted, give the player you made an offer on a large salary and wait for this offer to be accepted as well. This should get you the Wheeling and Dealing achievement as well.
Thanks to: Nighthawk205 (I copied a part of his comment for extra info)
I would make note that when you make offers on other players, make sure they've been with the team you want to make an offer to for at least a year or else the trade/purchase will be rejected.