Soft seeds?

One of my friends told me that soft seeds aren't any good. For example- any seed that you can place between your thumb and pointer finger and crush.

Is the softness of a seed any indication of it's quality?

yes man good hard ones are said to be best

I've heard the same... I'd assume it has something to do with the seed's maturity.

Fresh seeds have a waxy glimmer and a hard, intact shell.
Colours range from a buff through a dark brown, and from light grey to almost black colours. Often seeds are mottled with brown or black spots, or lines on a lighter field.

Green or whitish seeds are usually immature and will germinate feebly if at all.
Shiny, very dark brown or black seeds often mean the contents are fermented and the embryo is dead. Fermented seeds crush easily with finger pressure and are hollow or dusty inside.

Brick or compressed cannabis seeds must be checked as seeds that are bruised or crushed are not viable.