First thing to keep in mind: an enamel pin is a handmade product, which means it's often not 100% flawless, and can have very little (and often unnoticeable) defects.
I carefully quality check every pin before shipping and I divide pins by three grades:
A, B, C.
♥ A-GRADE (or standard quality) can have little to no flaws, such as small imperfection in the metal, tiny scratches, little black spots in the glitter, or unnoticeable air bubbles.
♥ B-GRADE has instead more noticeable flaws but still not too severe, such as missing enamel on some small parts, unfilled areas and tiny smudges.
♥ C-GRADE has very noticeable mistakes such as big areas with missing enamel or miscoloring.
When no further info is specified in the item options, it means the pin is a standard A-grade.
If you purchase a B/C grade, you CAN'T choose which flaws you "prefer", it will be randomic, hence prices are heavily discounted for these two type of grades.