How can you tell a good quality bag?

How can one discern the quality of a bag, ensuring that their purchase is of superior craftsmanship and durability? Are there specific indicators, such as material composition, stitching techniques, or brand reputation, that one should consider when evaluating the merits of a potential bag? Is there a universal standard for what constitutes a 'good quality' bag, or does it vary based on individual preferences and usage scenarios?