Bounty hunters are hired professionals by the police and government to mostly track and/or arrest dangerous criminals that violated their parole and such. I don't think they were wanting to or trying to kill the office guy, but the perpetrator was so happen to be in a car dealership to buy car in the office when the bounty hunters moved in to make an arrest. I guess they didn't know he carried a gun (illegally) with him when he started the shooting.
Perhaps I don't understand legal system in western countries. So far, I think to investigate or track down some case or person, you can do it in a secret maner, in which none police personnel can be hired to handle the case. But to arrest somebody, you need police (or else what are police paid for?), and in case it is not immediate criminal, you'd need a warrant from court to arrest someone.The guy pulled out a gun which then gives the excuse for the bounty hunters to use deadly force. As Equation said, it was incompetently handled by the bounty hunters.
For the US, where guns are spread when arresting somebody, you are expected the person to carry a gun, and always be ready for a firefight. When two arm men with gun ready in hands get killed by an unprepared person, it's rather stupid.