I'll try to explain again, Andy:
Being penalized for international market imports makes sense: it's money leaving your economy. Buying local/common represents value-added activity that benefits your country/enterprise or your direct partners. Great.
Exporting products to the international market, however, represents you GAINING value from people outside your economy. It's the holy grail of any economic system: bring in more money from outside the system, thus becoming wealthier. (In economics, recall, cash flows the opposite direction of goods.)
But in your scoring system you're penalized (negative points) both for buying from the international market (OK), and selling to the international market (NOT OK).
Experienced playing should be: buy local, sell global. Pay yourself to make the things, then get paid by everyone else for making the things as well.
Doing this
Common markets are pointless anyway. Even if they gave more score I wouldnt do it. The only score I care about is profit. Common markets wreck your profitability.
Don't use my current incarnation as an example but I know first hand it is possible to have a postive common market score and make money. But I do agree with john money over score
Creating a common market requires some effort, changes in products you and others produce and can increase your score.
There are indeed issues with profitability and we promised to look into it.
selling by default on the international market, is in Simcountry the easy option that always works and can be very profitable.
Something to consider for the near future.
There is going to be a resource 'shortage'. Not a market collapse, not a dooms day event etc etc resources will just become a bit harder to get.
If you have a large empire (10+ countries) it might become worth it to sell your resources on your own common market if this keeps your economy humming at full speed. It certainly is something I am looking into right now.
Oh yah. An oil apocalypse is coming to LU in around 100 days. Beware. I produce almost half of LU oil myself. It is going to be a big shock when all those corps close on the same day. Without oil, electric will get hit hard, which will then hit every other Corp.