it of course depends on the quality of the fabric they start out being- since charms are simply 5" squares cut from yardage-
if the yardage is a good quality fabric- the charms are going to be also-
if you purchase (name brand like moda or thimbleberries) from reputable quilt shops you will get good fabric-
if you buy them at wally world- or joannes- or some other big-box store chances are they are not going to be as good- and if you buy from ebay- or some place where you are buying from an individual---who knows what you will get
when you go to an lqs - charm packs are usually sitting on shelves- you can pick them up- touch them- see what they are...and most of the time see the fabric lines they go with too---so you can check out the yardage and see if they are what you really want.