u/Darkest_97

Is there a simple tutorial for how caravans to buy/sell to villages work?
I'm gathering the yellow number in the buy/sell screen is min price. I am unsure why I would ever change the slider? Would they ever buy or sell or for less?
I also don't understand the only options being 'Sell/buy all' or 'Sell from cargo'. Is it actually trying to buy/sell everything? There doesn't seem to be top up options? If I have 1000 flax I'd like to just sell until I have 500 or something.
I do not understand how to just buy or sell to a certain amount. Unless that isn't possible. I watched some videos but they all focus on outposts which doesn't help.