dog eat dog

Many would have come across a situation where sharpness of mind and quick reaction is much required. This is especially so in the sales and marketing industry - where it's fondly termed a "dog eat dog" world.
What I cannot understand is the absolute necessity for it.
I am on the camp that says - equal opportunities and professionalism.
As a department which relies a lot on advertisements - there would be a certain person we liase with over the phone for placements. Over time, rapport is built between this person and members of the department. Suddenly, when a huge advert appears, a dog comes barking around the corner, offering the department corporate services for future placements. When told politely that we are comfortable with the current arrangements, this dog went on to say that he could offer us artwork input etc, silly thing though, since the current person does the same.
Perhaps he missed the module that mentioned the importance of building rapport with the clients.
He must think he's some pedigree since he kept bulldozing his way into getting an appointment with me. Pedigree or not, on principle, if someone has been serving you for so long with no confusion, why change?
It's almost like how some banks work.
When you need money, they don't lend you.
When you have money, they want you to be their client.
It's a dog eat dog world.
He may need a new account to manage, but I'm happy with my current arrangement.
Although this lady may just be a tele-sales person, our account is hers, because she worked hard to gain our support. He may have a higher designation than her, but so what?
Let's be fair in work - everyone is earning a living - why do we have to grab income that isn't ours?