"When one player plays a negotiate and his opponent plays an attack card, the player who played the negotiate card gets to collect compensation."
So in your example, the Loser would technically collect compensation, but would draw zero cards since zero ships were lost to the warp. If you want the Loser's opponent to colect compensation, that would be a house rule.
For the sake of completeness, I should point out that there's more to the story than that. To collect compensation, you must
- reveal a negotiate card,
- be opposed to a player who reveals an attack card,
- lose the encounter, and
- lose ships to the warp.
If any of those conditions don't occur, there is no compensation (unless some other effect specifies otherwise, of course). Here are some more quotations from the rulebook (emphasis mine):
"When one player plays a negotiate and his opponent plays an attack card, the player who played the negotiate card gets to collect compensation. That player must randomly take one card for each ship he or she lost to the warp (not counting any allies’ ships – they go to the warp without compensation) from his or her opponent’s hand. If the player’s opponent doesn’t have enough cards to provide full compensation, the player takes the opponent’s entire hand of cards."
"Compensation is the term for cards a player gets to steal from his or her opponent after losing an encounter by playing a negotiate vs. the opponent’s attack card."
As for the other question, there are other powers and game effects that depend on what's in your hand. Some of these say you have to prove the contents of your hand, others do not. ... I would say unless the card or effect mandates you show your hand you don't have to show it. But that doesn't mean you're allowed to cheat!
Agreed. Some things in Cosmic work on the honor system, and some things require verification. Follow the specific text on each card.