^i agree, and i'll elaborate...
linings: if the garment is lined - check how it's attached to the exterior fabric - is it stitched in, is it partially stitched? worse - is there a cardboard or stiff fabric to give the cloth shape? this is a no-no, it creates unnatural lines in the fabric, creates awkward angles that your body could not possibly make in a garment. also - this backing over time and cleaning will stiffen or generate an unnatural shape to the garment.
fabric - always touch, don't look. read labels - what is the material? what are the care instructions? a higher thread count shirt will be lighter in the hand, almost like silk to the touch. it will cradle your hand,but when you let it back, it should have a clean hang with no depressions or ripples.
buttons - look for the shinier, harder buttons - you'll see them on quality garments - these are typically mother of pearl or another durable material - they won't break or let a sewing machine pass through. check for the stitching method - is it across or diagonal? how is the stitching finished on the fabric? it should all be clean lines.
on shirts - look for additional details - are the arms, shoulders and body attached carefully, or is it a front, back and a collar? if the shirt is patterned, do the patterns connect at the shoulder, on the back, on the sides? a quality handmade shirt will have interlaced patterns.
on shoes - look for the stitching on the bottom of the shoe - if the upper and sole are stitched, it's more durable. if you don't see stitching, it's probably glued. for the leathers, check the quality of the hide - if it's rough, it's synthetic or a cheaper hide. if it is soft to the touch, it could be higher grade (nappa). the softer, more supple leather scratches less than tougher leather.
also, when you're shopping - if the salesperson asks you for assistance AND you like the way they are groomed, manicured, neat in appearance, and properly dressed - ask them for their opinion on the clothing - if not, don't let them try to tell you anything about the garment. knowledge of what you are looking for and why empowers you over the salesperson, so you don't get bullied to buy.
it would probably help if you could tell us what kind of garments you might be looking for, then we could refine our advice. hope this helps