Local and common market is good?

Can anyone give tips

Used in moderation

It does increase your score and can help prevent shortages, but also can lead to over-supply and lost profit.

Selling to your countries isn't too difficult, properly suppling corps is time consuming.

Start with contracts to your countries of products that have severe shortages.

Does anyone know of a greater source of information on common/local market trading?

From what I've read online it can lead to shortages from unfulfilled contracts and will deplete your spending space with supposedly the only benefit being a small score boost.

I like the idea of paying my own money to myself by trading within my corp/country's but given differences in desired quality from Enterprise corps and Country corp/population consumption CEO's wind up handicapping their own output quality and Country's pay more than what they need for their own production/consumption.

Is there really any benefit other than Potentially +200 score?

Its great for keeping your ammo restocked on a monthly basis. Also if you contract weapons and additional ammo from your CEO (which is capable of higher quality) you keep the money in house and get the points bump.