Revealing Demand and Supply modifiers

I've been wondering how you've handled demand and supply modifiers during merchandile ventures. When my player enters a market, I've been allowing a Hear Noises check to determine the major exports and imports (any goods worth -2 or less and +2 or more). I don't give exact values, but should I?

I'm no Autarch, but my policy is to treat any demand modifier with an absolute value of 3 or more as stuff the player characters probably already knew as part of their general knowledge of the world. I let players learn demand modifiers with an absolute value of 2 if they make a good faith attempt to investigate the market in question (by, for example, asking travelling merchants about their experiences there), and let them know about demand modifiers with an absolute value of 1 and below only if they do a thorough in-depth investigation of the market in question (by, for example, living there for a few months and trawling through old trade records).

I don't generally bother giving exact values, but that's because my players don't generally care about the specific numbers beyond knowing if they're negative or positive. If they do someday ask, I'll tell them. (It's not like there's much they could do with that specificity of information, in any case.)

i haven't settled on a method i like 100%, but i have a rough framework that i'm trying out when players express interest in mercantile ventures:

first: as far as a player knows, everything in the region is at demand 0.

next: they can hire a sage for a month or do other things they make up with a similar cost/difficult to earn a piece of information.

you can spend a piece of information on one good in the region or one city.

when you spend a piece of information on a city, you learn 1 point of demand for everything in the city. so the first question you know what's in demand, what's in supply, and what's neither, but no degrees. the next time you get info on the same city, the >=+2 and =< 2- get separated from the +1s and -1s, and so on.

if you pick a good instead, you do a similar approach, but with one good in each city insteaad.

if you mix and match, you might quickly learn more about some goods in some cities.

all this aside, when you go to sell an actual good, you immediately learn it's exact trade value in the city you're selling in. 

Demand modifiers above +/- 3 should be well known to all in the city.  Whatever exports the city is known for should be known as well.  The info should be given to pcs who expend resouces for the info.  I like Jard's system but the question is how much?  

A sage costs 500 gp.  That seems a little much to get the scuttlebutt on market demand.  Also, general info on pricing should be easier to find out in a larger market.  Maybe something like this:

for 10 GP x market size and 4 days you 1 lvl of info      -   all mods +/- 3 or higher or complete info on 4 goods 

for 20 GP x market size and 1 week get 2 lvl of info    - all mods +/- 2 or higher or complete info on 10 goods

for 40 GP x market size and 2 weeks get complete info - all mods 

Venturers get the benefits of a larger market.  You can increase speed by 50% for 2x cost (3 days, 5 days, 9 days)


My own method of handling:

- Any character with Bargaining or Profession (merchant) can learn the demand modifiers for a city/town and its trade routes by entering the market

- Any character with a particular Craft or Labor proficiency can learn the demand modifier for their craft in a particular town by entering the market