l got liposuction 4 years ago but l never got the results l wanted. If l were to do it again could the same incisions be used?

It would depend on weather I thought  the placement of the previous incisions contributed to the lack of your expected results. I would certainly be cautious in darker skinned patient who form thick (hypertrophic) scars. Good luck. 

I am sorry that you did not have happiness with your first surgery.  Make sure that you and your PS are clear on what can, and can't be achieved with a second surgery. If the incisions are in a good position to access your current areas of fat, then the old incisions are best access.  If there are areas that cannot be accessed by the old incisions, others may need to be added.  Access scars cannot be eliminated, but talk to your PS about scar management to optimize whatever scars you have.  

That would depend on the areas to be treated. If the same areas are involved then possibly the same incisions could be used.  However, your surgeon may want to used additional access sites to improve your result.