Sellers may choose not to sell in certain markets if:
there are technological spillovers in the production of a good.
the social cost of production exceeds the private cost of production.
it is possible to practice price discrimination against customers.
the social cost of production is lower than the private cost of production.
buyers are unable to perceive the high quality of their goods.

the social cost of production exceeds the private cost of production.

Explanation:

The cost of natural resources for which the firms are not required to pay, for example, river, lake, atmosphere, etc. The use of public utility services such as roadways, drainage systems, etc. The cost of 'disutility' created through pollution (air, water, noise, environment).

When you issue a business or personal check, you simply write down the date the check is issued. The name of the person that will encash the check. The amount in words and in figures. Additional notes in the memo portion and then you sign it. Afterwards, you give it to the person you are paying.

The numbers on the bottom of a typical check represents the following:
1) Your banks ABA routing number. - specifies the bank and branch.
2) Your account number - specifies the account where the amount will be debited.
3) Your check number - specifies the number of the check you issued.

These are numbers which will be read by a clearing machine of the bank.