Buffer trail's are caused by bad technique and not working the polish long enough so that the abraisives fully break down. You will never remove swirl marks by hand, it is not practical as it would take a life time.
What you need to look for is when the polish goes clear, this means its fully broken down, machine speed is very important also. Its trial and error really sometimes letting the polish fully break down is not enough, you might have to spritze the pad with QD or water and let the polish work a bit longer. There is no wrong or right way, it takes as long as it takes and usually the working time is allot longer than people appreciate. A full car correction could easily take over 12 hours. You see it too oftern when guys run the machine over their car in a couple of hours and wonder why it looks terrible in direct sunlight.
Your paint usually suffers when the car has been in the bodyshop due to allot of them using harsh cuttng compounds as a quick fix, the usual punter sees a bit of shine on the paintwork and thinks its a good job, shame really but 90% of people would never notice the difference, most dont even see swirls