Trade companies are relatively expensive but they are very versatile and have several unique advantages.
They make exchanges with other players much easier and will also help you get around such annoyances as leader/mentor taxes and buying licenses to sell your items. If you are planning to invest some euro in the game (or have already done so) then trade companies are something you should seriously consider. Otherwise it may take longer to raise the initial startup costs, in which case you could start with a less expensive company or just continue to earn money as a regular alien hunter.
The main advantage of having a trade company is that you can buy or sell any type of item that can be made in the game. With all other companies except trade, we are restricted to only being able to sell things that are listed as "Products" for each particular company, and we can only buy things that are listed as "Materials" for each company. If we sell items as an individual (that is, without a company under our own usernames) we must pay leader, mentor, and income taxes on the amount of the sale, which added together can be around 40 percent. Individuals also must purchase licenses for whatever type of item they are trying to sell, and these licenses typically expire after one week. Trade companies also remove these restrictions; with a trade company you can buy anything from other players or other companies and then try to sell it on the market for a profit. The company does not need to buy licenses to sell goods, nor does it pay leader/mentor/income taxes on the sale amounts.
The other main function of a trade company is international trade -- that is, buying and selling items between different countries. Normally if you want to buy something in another country you would need to travel there and buy it on the other country's market, or list your items on the other country's market if you want to sell. Trade companies eliminate the need to travel to other countries for trading; instead we import and export things between other trade companies that are located in different countries. This is very useful for situations where there are significant price differences for goods that are located in countries that are very far apart, for example the UK and Indonesia.
In order to make a trade with another country, you need to find someone who owns a trade company in that country and then contact this player to set up a deal and agree on prices and quantities of whatever items that you want to trade. After you have reached an agreement, the player who is exporting (selling) the items can go to his/her trade company's warehouse, highlight the row for the item, click "Export", and then enter the data for price, quantity, and the six-letter symbol for the other trade company. After this is done, the proposed trade will show up under the "Proposals" tab for both companies.
After the proposal is made, the trade company that is importing (buying) the goods will need to accept it before the money and goods are exchanged between the companies. For international trades, it is also necessary for both companies to have at least one customs document in their inventories (listed under "Products"). Customs documents can be made by the trade companies and require two units of paper as "Materials". Paper is relatively inexpensive and can be bought from the game if none exists on the local market.
When exporting goods from your trade company warehouse you can also check the "International offer" box instead of entering the symbol for a specific company. This will place your goods on the general market where all players in all countries will be able to see them when they access the market and click the "International offers" button near the bottom of the page. If someone who has a trade company sees your offer and agrees with the price and quantity, that player can accept the offer and have the game create an automatic proposal between the two trade companies. When the importing player accepts the proposal (found under the Proposals tab of the trade company) the goods will be transferred to the importing trade company and the exporting company will receive the gold (any applicable taxes will be automatically deducted).
Trade companies can also make all of the licenses that players need in order to sell items as individuals. These also require two units of paper and have about the same production costs as customs documents. In order to make either licenses or customs documents you will need a machine (the "trade machine"); however, you do not need a machine to simply buy and sell things on your country's local markets.
Trade companies hire workers only when making licenses or customs documents. To do this, you simply need enough money for wages and enough materials in stock, after which you can activate your workplace to post a job listing just like with any other company. Workers are not needed for buying or selling items.
