Quality refers to flavor, texture, and color.  The sugar content is of little value in measuring quality since all dates that are acceptable in other respects have adequate sugar content.  In general, dates should be soft and texture smooth.  But perception of flavor, texture and color all are subjective, and vary from person to person so that no certain criteria can be provided.

There is an inexpensive method of  softening dates by activating a natural enzyme of the fruit.  the process increases the moisture content of the fruit  and exposes it to moderately high temperature, activating the enzymes, which are then later deactivated by drying the dates to the normal moisture level which prevents further change.