Experienced hitman are probably extremely rare outside of the narco cartel world. Thus, I would say that if it were an arranged 'hit', the murderer was not experienced.
As for being an experienced shooter..... studies have shown that the abilities of even experienced paper target range shooters can deteriorate significantly in real world situations. Therefore, it could be impossible to tell if the shooter was an experienced range shooter or a novice.
Looking at the footage, the shooter did manage to hit the victim four times while under stress. This could point towards an experienced shooter. Then again, the range was very close and the shooter did not seem to be using advanced techniques such as trained stances, 'double taps' etc. This could equally indicate a novice shooter who got lucky.