Hi there- I think it's important to start with the basics you would check for in any physician- where did they go to school, where did they train, and for how long... The next tier of your research should be a bit more specific to the present goal- Are they board certified? By whom?
For this type of procedure I would definitely want my loved ones being operated on by a surgeon Board Certified by The American Board of Plastic Surgery. This tells me that they completed a 5-8 year residency training program IN PLASTIC SURGERY (not in some other specialty), and that after this training, they passed a comprehensive and multi-year examination of their knowledge, judgement, and practice quality.
I think most people would agree that having a surgeon who learned to do liposuction (of any kind) over a period of years, under direct supervision by a board certified plastic surgeon, is more likely to give you the outcome you want than if performed by a doctor in another specialty who learned to do liposuction in a weekend course somewhere (no matter what machine they use).
Once you're comfortable that you are dealing with a surgeon Board Certified by The American Board of Plastic Surgery (do ask- some doctors skirt this issue by telling you they are "board certified", but deliberately leave out by whom), ask how many cases they have done with the VASER. Experience with the device in question is important, but not nearly as important as the above.
Finally, it is very important to realize that while the VASER is a fantastic tool (I personally believe it is the safest and most effective tool for improving the body contour available- and I have used them all), it is the surgeon at the end of the instrument that will matter most to your outcome.
Too often I meet patients who seem to think that the machine is most important- when nothing could be more wrong. Think of it this way- if I put you behind the wheel of Michael Schumacher's Formula 1 racecar, do you think you would win any races? I doubt it. It's a very nice car, and certainly a factor in his success, but let's be honest- the driver is more important. This is really not much different- The VASER is an awesome tool, but having a surgeon who knows how to use it effectively and safely is more important. I hope that helps you. Good luck in achieving the body contour you dream of!