There should be quality standards available from your supplier that manufacturer uses. Cracks are never acceptable and would not be considered a defect. The root cause may be a defect but a crack itself would be caused by contact or rough handling. Our glass container industry rates defects into 3 basic categories. Major - These would cause harm to the consumer; Minor - These will effect the way the bottle performs during production; Cosmetic - Visually the container doesn't look correct but defect does not effect container's use. Overall all defects, which there are far too many to list, generally should never exceed 1/2 of one percent of a total production run. This would not be your particular order unless your order included every bottle produced. Any good supplier should be able to determine what the cause of a crack was and determine if the root cause was a defect. If you would be interested in getting a hold of testing lab to determine your particular issue I would suggest getting a hold of the Glass Packaging Institute. http://www.gpi.org/