Why don’t the Cadaver Collector, Eladrin, Skull Lord, Sorrowsworn, Steel Predator… have save proficiencies?

How adventurers can evaluate the value of looted items ?

Does Sneak Attack or Colossus Slayer triggers Hunter’s Mark each one?

2 elves in my party near mutiny thanks to long rest RAW

you can download Sage advice compendium here:

http://media.wizards.com/2016/downloads/DND/SA_Compendium.pdf

In Curse of Strahd would you stop a character from simply taking every dark gift?