Role of the consumer as a ruler of the market?

As the ruler of the market the consumer is supposed to indirectly tell the producer what and how much of that item they are supposed to make. They do this buy buying out an item that they really like which tells the producer that they need to make more and can possibly charge more for that product since so many people want it so bad. On the other end of that,  when consumers don't purchase the product that is being sold then producers will either charge less because the price they have it listed for is too high or they will take the item entirely off the market because they are not making any profit off of it.

the answer is: must pay taxes on profits

since it is considered as a part of your income, profits from investments is eligible for tax payment.

the tax from your investment could be influenced by how long you decided to sell it. united states promotes keeping your investment for long term period. so, the tax rate for investments that you sell in less than one year is typically higher compared to investments that you sell in more than one year period.

necessary and proper clause. the congress shall have power to all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states, or in any department or officer thereof.