I'm not quite sure if this is a gross game logic error (part of the many in the game)... Refer to original post in the PC issues board: http://www.gamesas.com/index.php?/topic/1123362-how-quickly-is-reputation-suppose-to-change/

If that's how quickly reputation changes in the game, then it definitely needs to be fixed. Overall reputation changes should be a bit slower with random encounters outside of faction turf having little to no effect on reputation shifts. Killing two Powder Gangers in the middle of nowhere shouldn't change your reputation much at all, since there were no witnesses. The only time reputation should really change due to infractions is when you are in areas owned by the faction or near any witnesses.

Know what else doesn't make sense? I kill two powder gangers and gain rep, then lose karma for 'stealing' all of the ammo in their camp.

Aren't these violent ex-convicts raiding the town? Why am I losing karma for taking their stuff?

Despite that... The owner is dead now. Is it really stealing when the owner is dead... And that's not considering if it wasn't your fault they're dead in the first place.

And yet I get no karma loss for digging up all the graves in the cemetery and taking the stuff they're buried with.

Well, I did some looking around and found the offending game setting and corrected it. Now negative reputation shifts happen much more slowly. Here's the mod: http://www.newvegasnexus.com/downloads/file.php?id=34944

I took the cost for a major faction crime and changed it from the bloated 30 setting and dropped it down to 7, so it's in balance with the major good stuff reward that's also 7. As a side note, sneak attacking people seems to not trigger a crime. Might be something to investigate in the future for when you take attack random spawns and leave no witnesses.

I only have it as a hot fix of sorts, but may be interested in working it a bit more into something more significant... Once a few more patches roll out and things stabilize.