Back when I bounty hunted for a while I never needed a group (the profession is based for 1v1 encounters), never wanted a group (they give you away easier and it is harder to decieve the target), and a same faction group cannot always kill your faction and it only works if the target is even overt.
As a bounty hunter you don't need a group. You should be able to take anyone out as long as you know your class well, know their class well, and you have good buffs/equipment. When I bounty hunted I had decent equipment, so I made up for it with wits. I decieved my targets, and the ones that couldn't be decieved I waited until the prime moment to strike. I'll list two examples:
I was level 64 at the time, had a LLC + capped composite and a bomb droid. I walked up to the target and initiated conversation, acting like I wanted to be friends. He bought it and began distracting himself with his inventory. While I was talking, I was waiting for the moment to say "lol", my bomb droids attack command. Right when that moment hit, I hit him with everything I could. Once his health got to half way (in about a second or two), he began to realize what happened. But it was too late, I finished him in about five more seconds (this is why paying attention is vital). I took about 3k or so worth of damage.
The second time, I was in my 70's I believe. I went into DWB after the target, asking to group. The guy ignored me and cleared the way, so I followed him in. He began attacking some black sun and got into a fight with two or three of them. That's when I attacked and finished the guy in a few seconds, completing the bounty and I cloned at the Smuggler's Outpost (black sun aggroed because of my low combat level).