Minecraft Dress and Outfit Skins

A dress is the one garment the player model actively fights, because the legs are two separate boxes with a gap between them and there is no skirt geometry to paint onto. Skins solve it by drawing the skirt across the front and back faces of both legs so the gap reads as fabric folds rather than a hole, and the good ones line the pattern up across both legs so it does not break in the middle.

That is the thing to check in the previews below: look at where the two legs meet and see whether the skirt pattern continues cleanly. It is the clearest difference between a carefully made outfit skin and a quick one.