Vetting cosmetic surgeons is a very tough job because of information asymmetry. It is hard to know what you don't know.
First, recognize that no one specialty is exclusively qualified to practice liposuction. Malpractice data from Florida in fact indicates that you are probably much safer having liposuction with a dermatologist than with a general plastic surgeon! The two largest specialities offering liposuction are dermatologists and general plastic surgeons. There are other cosmetic "surgeons" out there practicing liposuction and doing a great job but it gets harder to generalize what you should look for in these individuals to assess them.
Second, the type of liposuction practiced by dermatologists and general plastic surgeons differs. Most dermatologist are performing liposuction under local anesthesia which turns out to be much safer than having liposuction under general anesthesia. In contrast, general plastic surgeons prefer to do liposuction under general anesthesia. It is a cultural thing. Plastic surgeons like their patients asleep under general anesthesia, and dermatologists are much more comfortable with their patients awake and talking. There are now an ever growing list of laser liposuction machines. These do not appear to offer any advantage over standard micro cannula tumescent liposuction other than marketing allure.
If you are looking at a dermatologist, they should be board certified in dermatology and have completed a dermatologic surgery fellowship. It should be clear from their marketing that liposuction is a big part of their practice. Dermatologists generally do not seek hospital privileges in liposuction and they typically don't need to admit their patients because of the inherent safety of the liposuction they practice. Plastic surgeons should be board certified. For this speciality it would be a red flag if the plastic surgeon did not have hospital privileges in liposuction. Both types of surgeons should have medical malpractice insurance for liposuction.
For all surgeons, check with your state medical board to learn if they surgeon has had disciplinary action taken against them in the past. Any surgeon can be sued for malpractice but numerous judgement are a cause for concern. If available, review the surgeon's curriculum vitae. What you are looking for are obvious gaps that might indicate they did not complete their training in a routine fashion. This might be a sign of behavioral problems that resulted in being fired from a residency program, drug rehab, and in some cases prison time.
Finally, do your home work. Visit with the surgeon for a consultation. Do they make sense, do you like them, does the staff treat you well? This should help you in vetting a liposuction surgeon.