You made a promise to pay for the car when you got it, and obviously you did for awhile and then something changed in your life that made it difficult or impossible to pay, but how does that equate to them scamming you? You needed a car for work, school, errands, etc. and I'm willing to bet this isn't the first time you've had credit problems and you promised "this time" you would make the payments and the bank trusted you to do so, you signed something saying you would and would also be responsible for any fees, repo costs, etc. True, banks and the gov't are in bed with each other, but that doesn't give YOU the right to walk away from a car and expect nothing to happen! The $4000 is the difference between what you owe and what they were able to sell the car for at auction, who do you think should be responsible for it? This also tells me that you got the car at 100% financing and did not put any money down, or else you would not have this deficiency when you gave the car back.
Unprofessionalism? YOU are the one that promised to pay and are backing out of it, so YOU set the precedent of how things are going to go down, so if you YOU decide you are going to not fulfill your end of the contract, why should they? Much less, you are a non-payor and why should they be nice to you?