2. This contract differs from a sale in this, that barter is always of goods for goods, whereas a sale is an exchange of goods for money. In the former there never is a price fixed, in the latter a price is indispensable. All the differences which may be pointed out between these two contracts, are comprised in this; it is its necessary consequence. When the contract is an exchange of goods on one side, and on the other side the consideration is partly goods and partly money, the contract is not a barter, but a sale. See Price; Sale.
By default this option is turned off. When you load the mod menu, the value you see displayed is the setting currently in use in your game. The vanilla value is 2.0, so any other number indicates that another mod is already changing this setting. If you decide to turn this option on, than the settings from Trade & Barter will overwrite any changes to this value made by other mods. If at any time you wish to revert the settings back to those made by another mod, simply toggle off this option and reload your game. You will need to reload your game before the changes from Trade & Barter are fully canceled out.