A collar advertisement

Most tragic of all is the person with real gifts which could make him a success, but who remains a failure because he has never developed them. A handsome young man, who looked as if he had stepped out of a collar advertisement, once came to see me. He explained that he got one excellent sales position after another, but he never seemed to satisfy the expectations of his employers. After a short while he was always dismissed.--by Salter

Hello,

Could anyone explain the connotation of "a collar advertisement" here? It seems he was very upset.

Why did the author especially use "collar" instead of any other product?

Thanks!

PS. Reading further, I found actually that refers to how handsome the man is, though, I am not sure if I'm correct. What does a collar advertisement refer to? Do they advertise collars using handsome models?