I will note, first, that I tried searching for a similar suggestion, and none of the threads I looked in had something like this. If I missed one, sorry.
The liaison is spammy and worthless and it should be (in a free market economy) simple to say how much you will pay for an item.
There is no haggling, either the other side want's to send goods at the price you set, or they don't. Simple as that.
Doing business without haggling is a recent innovation. Trade is subject to two things: how badly the recipient wants it, and how hard it was for the caravan to get it(demand and supply, respectively). In modern times prices are set, but historically that wasn't always so.
But even if it were, the trade liaison's meeting is not just a simple sales transaction. You have goods you want, and you want to get a low price for them while still making sure you get enough. The merchants have a similar agenda of their own. Both of you are trying to get the lowest prices for the things you buy, and the highest for the things you sell; and the agreement you reach sets prices for
the whole year.
So maybe the spam can be toned down, but the liaison being there makes perfect sense. And trade agreements will be even more significant if, say in the caravan arc, more than one merchant from a civ starts coming per year(without triggering multiple liaisons).
We don't need to be interrupted 4 times and adjust the sliders every time for the liaison when the poster is right, we could easily send a paper stating what we will pay for an item with the caravan. And they can send one with the caravan stating what they will pay for certain items.
I think the only time the liaison screen should come up is if we DON'T have those sliders set in a sub menu (As kinda a noobie protection) and it should tell us that we should adjust them because it strengthens bonds or some such.
Getting rid of the sliders in the frequent meetings with liaisons is exactly the point, though I still say that from the perspective of your dwarves, they ARE conducting negotiations. If your broker(or leader, for dwarves) is better at getting his/her way, you'll get a deal that's better for you - but mercantile between civilizations is rightly a matter of negotiation. Just because the actual haggling is done by the dwarves without being explicitly depicted(especially with non-liaison civs) doesn't mean it isn't there - and it
belongs there.
But yes, a simple "The meeting with the liason has started - you may now make requests to the liason by accessing the Trade Depot" message would be vastly superior to the spammy "black screen, five seconds wait, sliders, black screen, five seconds, sliders" system we have now.
Well, not exactly what I have in mind, though it raises an important point. I'd intended that you could access the trade preferences through {n}obles -> {s}ettings on your broker at any time. It is worth advising the player, when negotiations begin, that it's the last chance to do so before the contract is set for the year - in the form of a message in the normal scroll, most likely. Though if the player has never touched that screen, an initial greeting message(like the one that exists now, but with the added advice to go into the {n}obles screen to change these settings, or possibly an option to go directly to the settings screen from there) followed by the usual delay would be good; and after this delay, you are presented with the opportunity to inspect both the import and export agreements, and there see any prices which are not standard.
Doing them both consecutively, rather than with the pause that exists now, would make the liaison that much less troubling.
Even if the meeting itself winds up taking just as long, removing the player interruptions(and the bug that lets them progress while, say, plotting an exploratory mining shaft or the new expansion of your living quarters) would make the process less aggravating.
Oh - and maybe increase the meeting priority at the same time(but still let "Trade at depot" trump it).