Because there is no general rule for it online(that I have found, anyway), I am going to write up a small system of commodities price generation… shouldn't be that hard really, expecting most of it to be pretty basic…
FARMING
Most commodities in this area fluctuate on the basis of supply and demand of the market. For the sake of argument, there are three basic commodities that can always be bought at a profit, as long as they are traded at a different town: Grain, Spices, and Ale. Here is a basic chart to map prices based on NPC reaction.
Profitable Goods:
| Comodity | Purchasing Price | NPC Reaction (25%) | NPC Reaction (50%) | NPC Reaction (75%) | Item is in short supply |
| Grain | 3 Silvers | 3 SP, 1 CP | 3 SP, 3CP | 3 SP, 5 CP | 5 SP |
| Spices | 1 GP | 1 GP, 5 CP | 2 GP | 2 GP, 5 SP | 6 GP |
| Ale, per Keg | 1 GP | 1 GP, 1 CP | 2 GP | 2 GP | 4 GP, 5 SP |
As for other saleable goods, here is a quick shart comparison:
Common Goods:
| Commodity | Purchasing Price | NPC Reaction (25%) | NPC Reaction (50%) | NPC Reaction (75%) | Item is in short supply |
| Keg of Good Wine | 20 GP | 19 GP | 21 GP | 24 GP | 30 GP |
| Keg of Cider | 8 GP | 7 GP, 5 SP | 9 GP | 11 GP, 3 SP | 14 GP |
| Salt, Per lb. | 1 SP | 9 CP | 1 SP, 3 CP | 2 SP | 4 SP |
| Preserved Fish, Per 100 | 1 GP | 9 SP, 5 CP | 1 GP, 5 SP | 2 GP | 3 GP, 5 SP |
| Preserved Meat, Per Keg | 1 GP | 9 SP, 8 CP | 1 GP, 6 SP | 2 GP, 1 SP | 4 GP |
| Rice, Per lb. | 2 SP | 1 SP, 5 CP | 2 SP, 5 CP | 3 SP | 5 SP |
| Coarse Sugar, Per lb. | 1 GP | 9 SP, 5 CP | 1 GP, 5 SP | 2 GP | 4 GP |
| Cheese, Per lb | 8 SP | 7 SP | 8 SP, 2 CP | 1 GP | 2 GP, 5 SP |
You'll probably notice that most of these, the Reaction (25%) is slightly lower then the actual sale price. I go with the theory that if the merchant does not respect the characters, or dislikes them, he will do his or her best to cheat them. This also goes the other way. If you really wanted to be insidious, you could have the merchant sell the characters barels of rare spice cut with something… for example; pine needles…
To figure out if a commodity is rare, I assign each item in the list a series of numbers between one and ninety-nine, and then roll a percentile three times. The items that come up on the percentile roles are in the short supply category. If the character is at least at 50% reputation, I give them the short supply column. If they are below, I give them the 50% collumn. Even if the merchant is angry, he will still give them a slightly reasonable price.
For figuring out the merchant's reaction, I do a charisma check versus a DC 15 plus the negotiating party members modifier, plus a number of special circumstances listed in this table
NPC Reactions:
| PCs are helping the town defeat a Villain | +5 | PCs have been spotted working with a villain | -5 |
| PCs are carrying much needed goods | +4 | PCs have killed town members or guards | -4 |
| PCs are carrying a banner to the King | +4 | PCs are carrying a banner to the hated monarch | -4 |
| There is a Paladin in the Party | +3 | There is a obvious Necromancer in the party | -3 |
| The negotiating character is of opposite gender | +2 | The characters cannot speak the merchants native language | -2 |
| The characters give a proper greeting in the merchants native language | +2 | The character's weapons and armor are covered in blood | -1 |
| The characters have many items of interest for the merchant | +1 | The characters are selling merchandise from this town | -1 |
| The characters have had positive dealings with this merchant before | +1 | The characters are in possession of a obvious slave | -1 |
For example, a party of PCs approach a merchant. There is a Paladin in the party(+3), but the characters cannot speak the merchants language proficiently, and fumble the greeting(-2). Their weapons and armor are covered in blood from a recent battle with goblins(-1), but they are carrying much needed goods(+4). The party spokeswoman approaches with a charisma modifier of +3. The equation is (15 - (1 + 2) + (3 + 3 + 4)) = DC 22. The merchant has a charisma bonus of +3, which pulls the DC down to 19.
Now, for each 5 points the merchant fails by, his disposition goes up by 25%. However, for each 5 he succeeds by, his disposition goes down 25%. If it is neither of the above, the disposition is 50%. Now, for this scenario, I rolled a 13. That would mean the merchant failed by one point, meaning his disposition is 75%, getting the second best price. (Note: if the merchant fails by 10 or more, I allow the characters to make a diplomacy or bluff check to get the rare goods price.)
