How to tell if a dress is well made?

Turn the dress inside out. If it looks just as good inside and out, it’s good. Lining coats and jackets with silk instead of synthetic fabrics. Silk linings are more delicate, but more beautiful. Good things need to be carefully maintained. It’s a personal choice.
Check the fabric: the check or stripes should be straight. Look at the stitching: Is the thread loose? Is the hem flat or drooping? Are the buttonholes neat? Are the buttons tightly tacked on? If there are loose threads, it means it was machine-made, and machine-made buttons tend to fall off eventually. Buttons that are hand-made are more secure. Also, pay attention to the material of the buttons themselves: Plastic buttons are stronger than mother-of-pearl and glass buttons, but they don’t look as high-end. Mass-produced clothes are made for speed, so the workmanship is sloppy. Unfortunately, well-made clothes look exquisite.