(1) How deep the scarring is in the skin (deeper scars require deeper peeling to affect improvement)
(2) What kind of procedure the patient will tolerate (anesthesia or not)
(3) Expense (varies from under a hundred to thousands of dollars a treatment)
(4) Healing time (a few days to weeks)

Pretty much what you should do is get a few opinions to see that which is suggested. Most patients start with something light such as light chemical peels as they can be done cheaply and without anesthesia or much recovery time. The deeper peels make you look kinda like a burn victim for a week or so, but offer much more improvement for deeper scarring.

Laser re-surfacing will in general cost more, but can offer the most dramatic improvement and take the longest to heal. Microdermabrasion is probably equivalent to light chemical peeling but tends to cost more.