Why is there no Word Games Forum or Subdomain?
There should be a Word Games Subdomain, or at least a Word Games Forum!
So with a negotiate a colony or card has to be traded as part of the deal, but what else can you do in a negotiate to sweeten the deal?
Up to one colony, and any transference of cards. That's it.
I know you could do things like agree to ally with the other player next time they are defends or agree to play a flare card that may benefit them on their next turn.
Actually, by the rules, you can't.
However, there's more to trading cards than just offering cards: You can offer to receive any cards the other player doesn't want. You could specify number of cards, or their types, or their specific values. They can be specific cards or random draws.
What other things can be done during a negotiate and what would not be allowed in your opinion?
The Zombie can free the other player's ships from the warp. It's possible that other aliens published in the future will allow other things to be traded.
You can't trade anything you don't own, such as cards from the deck.
You could house rule a number of additional trade commodities, such as Tech cards.