The salesperson will give you the deal that the sales manager dictates and approves.
So when your negotiation skills fail to move that number, the sales person is the **** of the earth in your opinion.
And you are entitled to that opinion but consider this -
The dealer salespeople and managers do this everyday all day long and year after year.
That's a ton of knowledge of the car business and retail sales experience.
Your salesperson may be selling 20 cars a month while you are out to buy your first vehicle in 5 years.
It never was a level playing field.
One guy goes home thinking he got a bad deal, another brags to friends about the great deal he got.
What is a good deal; what is a bad deal ?
No one has ever known. It's PERCEPTION determined by the buyer.