Local and Common Markets

I know these questions have probably been asked and answer already, but I cant find it. So here goes

1. What are the benefits of using the local markets only?
2. What are the benefits of the common market?
3. Does using the common market decrease my corps sales and profitability?
4. What price do I get paid and pay when using the common market(Buying and Selling), the market price or my marked up prices?

Can you give detailed answers please.
***I will continue to post questions as they come up

1. common markets are good when there is a shortage of items you manufacture and you can sell to your country/corps so there is no shortages on ur part

2.Does the same as #1 just widens the amount of things for contract

3. I dont really know kinda new

4. market price

1-2.
In addition to covering shortages, the common/local market also benefits your score. There is still some degree of ability to bring in an attempt at averaging quality between supplies, but not to the extent there was before recent changes.

Local market is simply trading among your own corporations. It increases your score, but if your purpose is to integrate with others, this might not be what you want. In all other ways, the common market and local market can be treated as one thing.

3-4. Common markets pay the market price adjusted by demand with quality taken into account. So, the price your local market pays are exactly the same as the price the product would get on the world market. But, as common market quality can be very high (over 300) you may be buying supplies at a quality you don't want to pay for. Quality greatly affects the price. You can also cancel common market contracts from corporations