What is the ruling on sewing and tightening abayas, and selling embellished and fitted abayas? And is there sin upon the one who does that?

If you are certain or it is highly probable that women will wear tight or ornate, eye-catching clothes in front of non-mahram men, then it is not permissible for you to sell or tailor such clothes for them, as this constitutes cooperation in sin. However, if the prevalent use of these clothes is permissible, such as wearing them at home, then the original ruling is that selling and tailoring them is permissible.