The amount you receive in overseas profits is calculated as a percentage of the purchase price paid by the buyer. If you have the best possible diplomatic relationship with the Tribe which produces the commodities you will receive back 100% of the price. In this case, if you buy the product, the entire amount you paid is returned to you--so you get the commodity for free.
If your relationship with a Tribe is very bad, you will receive very little profit on the sale of the commodities you developed. You can improve your relationship, and the percentage of each sale you receive, by making more trade deals with the Tribe. Even the deals which only happen because you developed the land, and bid on the commodity from it, improve your relationship.
Generally, your country’s position on the relationship spectrum with the Tribe selected on the diplomacy screen is a good guide to the level of overseas profits you will receive. If your country is denoted about halfway up the spectrum, you will receive about 50% of the sale price.
