What rewards are considered higher quality?
In Ghost tree, Lucky Charm gives you an increased chance of getting a higher quality item as a reward on payday card draw.
Which items are considered higher quality? Are different weapon parts also in quality order?
The lucky charm perk increases your chance of getting infamous items (Special masks, patterns, colours and materials).
By how much it increases your chance is not clear, as of yet. There are, however some speculations about it (see links).
How useful is lucky charm?
about lucky charm skill