How do legal contracts provide incentives for people to exchange goods and services?

Legal contracts provide incentives for people to exchange goods and services by allowing fair trade and consequences to come into effect if one party doesn't meet the legality of the contract. Both parties of the exchange are given guidelines to follow as well as the rewards and ramifications of certain actions

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

producing or giving rise torelating to or engaged in the production of goods, crops, or other commodities.

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.