Screen shots are valid proof within the situation.
I.e A player disrespecting you ingame - Screenshot of the disrespect and the steam id
Screenshots will not be valid in cases.
I.e Rdming, Unless its a gif/video. The situation will not be shown and the context could be missed. Maybe you misunderstood the staff/owner or they misunderstood you.

Screen shots are valid proof within the situation. I.e A player disrespecting you ingame - Screenshot of the disrespect and the steam id Screenshots will not be valid in cases. I.e Rdming, Unless its a gif/video. The situation will not be shown and the context could be missed. Maybe you misunderstood the staff/owner or they misunderstood you.