I think that player Scavs who kill other AI and player Scavs should start with a knife only. Not only that but the time for being to play as a Scav should be increased. First offence maybe a 1-3 hours and if this happens consecutively then this doubles every time.
This is only part of what I believe would be effective. I'm not sure on what should happen to your PMC and the relationship with your PMC to the traders.
The more penalties you add to player Scavs, the more it becomes a deterrent. I always try to befriend fellow player Scavs and about 90% of the time I could have killed them several times over but I'd say 8/10 - maybe 9/10 they shoot at me and usually I will lose these fights as I'm reacting to their reaction. My stash is full and I have plenty of money so it's not so bad for me but it still annoys me every time as I could have easily killed them while trying to get their attention.
Anyone killing player Scavs as a Scav themself, be ashamed of yourself. It's not that you're better that you're winning fights with people, it's just that some people are intelligent enough to know that if they work together they will get a lot better loot than the Scav gear so they try to work together for a better payday.