Indian Head Cents Grading

To begin, mint state grades could almost certainly be crossed off with nicks. As a rule, look at the diamonds in the headband of the Indian obverse. The more defined, the higher the grade. I would strongly suggest buying ANA's Photo Grading Standards or Coin Worlds Making the Grade. Both books have full color images and text descriptions of each grade, for all denominations/series of U.S. coinage.

There are many factors that determine a grade, including wear, eye appeal, and other major distractions in the coin. It is difficult to put a simple answer out there on the grade and how many dings there are.
Major scratches, cleaning, and environmental damage are example of what can earn a coin the details grade. Luster can play a role, especially in eye appeal and cleaning. But not all coins wear the same, so you have to pay more attention to wear than luster.

Indians with nicks generally don't get MS grades. With pics we can give better estimate of the actual grade. Early in the year I sent a few IHC to get graded, I was close on most but off on 2 out of 8 coins I submitted. 2 were details but I hoped they would straight grade, when you think it's details chances are good it's details.