This is education, not advice
The information here is written for the general reader and does not replace a personal medical consultation. It cannot tell you whether the tissue on your arm is fat or skin, or whether an operation is appropriate for your health or your circumstances.
No outcome is guaranteed
No treatment can be guaranteed. How much an arm narrows, whether the skin takes up over the new contour, and how the entry-point scars settle vary between individuals, and the result is judged honestly only after six to twelve months.
Scars are permanent
Arm liposuction leaves small scars where the entry points are placed, and a skin-removing operation leaves a long one along the inner arm. They mature and soften over a year or more, but they do not disappear, and no surgeon can promise that they will be invisible.
The limits of a small site
The arm is a small-volume area under thin skin, and the change that can be achieved is correspondingly modest. Anyone describing the operation as a route to slim arms is describing something it does not do.