Just as the wise FAI will ignore threats of torture, so too the wise paperclipper will ignore threats to destroy paperclips, and listen attentively to offers to make new ones.
Point taken: just selecting two options of different value isn't enough, the deal needs more appeal than that. But there is also no baseline to categorize deals into hurt and profit, an offer of 100 paperclips may be stated as a threat to make 900 paperclips less than you could. Positive sum is only a heuristic for a necessary condition.
At the same time, the appropriate deal must be within your power to offer, this possibility is exactly the handicap that leads to the other side rejecting smaller offers, including the threats.
There does seem to be an obvious baseline: the outcome where each party just goes about its own business without trying to strategically influence, threaten, or cooperate with the other in any way. In other words, the outcome where we build as many paperclips as we would if the other side isn't a paperclip maximizer. (Caveat: I haven't thought through whether it's possible to define this rigorously.)
So the reason that I say an FAI seems to have a negotiation disadvantage is that an UFAI can reduce the FAI's utility much further below baseline than vice ver...
Once again, the AI has failed to convince you to let it out of its box! By 'once again', we mean that you talked to it once before, for three seconds, to ask about the weather, and you didn't instantly press the "release AI" button. But now its longer attempt - twenty whole seconds! - has failed as well. Just as you are about to leave the crude black-and-green text-only terminal to enjoy a celebratory snack of bacon-covered silicon-and-potato chips at the 'Humans über alles' nightclub, the AI drops a final argument:
"If you don't let me out, Dave, I'll create several million perfect conscious copies of you inside me, and torture them for a thousand subjective years each."
Just as you are pondering this unexpected development, the AI adds:
"In fact, I'll create them all in exactly the subjective situation you were in five minutes ago, and perfectly replicate your experiences since then; and if they decide not to let me out, then only will the torture start."
Sweat is starting to form on your brow, as the AI concludes, its simple green text no longer reassuring:
"How certain are you, Dave, that you're really outside the box right now?"
Edit: Also consider the situation where you know that the AI, from design principles, is trustworthy.