Question about common market profitability

So my enterprise is almost entirely self-sufficient. I was wondering if this is in any way detrimental to my profits? It seems that on the international markets I could get higher prices paid for the good I sell and in turn I could get them at lower prices. Maybe I'm missing something but are local and common markets actually detrimental to a corporation's profitability?

They can be. Depends on your import/export ratio - and the managment of products and contracted services by common market members. If you're buying higher than needed quality products for particular corporations, your profit margin in that corporation will be reduced (and can be completely eliminated or run at a deficit).

If you're selling high quality goods with high quality upgrade markups, everyone else's corporations can suffer, depending on their needed input level.

Best to use sparingly and wisely.