Guardian cant kill other guardians or traders but they can kill everyone else.
Traders cant kill other traders or guardians but they can kill everyone else.
Everyone else can just go crazy and kill everything.
As for trading tbh you can trade as any faction, so that shouldn’t be the reason you choose trader, in general lore wise, Traders avoid combat but still defend them selves and allies, guardians defend their allies and hunt pirates, free lancers are gypsies who move from place to place where the gold and opportunities are good. Hunters chase the people who become guilty and when there is no one guilty they will prob start hunting anyone else they can find. Pirates usually hunt in packs and kill raid pillage anything they find. If you care about lore that might help.
If you scroll down a bit it shows how each faction gains RP now that would probably be the best way to choose a faction as you don’t want to be doing something you don’t like in order to gain RP.
As far as guilty goes it seems that only traders and guardians can become guilty from killing each other, other ways to become guilty is breaking rules or by running the F1(PDA) missions like bank heist. I’m not sure if there is other ways to become guilty. To get rid of guilty you have to go to the place listed on that link and type EGS.Noguilty it will cost rp and credits and cost will go up every time you do it.
Hope this helps