It's been years, so I'm having trouble remembering the exact mechanics, but I recall it being non-trivial to continually murder PCs while maintaining a positive reputation. The most efficient way to do this would have been to kill dragons, and you needed to be a "tamer class" to do that efficiently. Most PKs weren't tamers. Also, having 5+ long term murders and a "red" name floating above your character was a dead giveaway that your character was up to no good.
I felt the system was brilliant and going on a PK hunt was the best fun ever. My brothers and I played UO from the moment it came out for another ~4 years (basically to whenever the non-PvP stuff came out, that turned us way off from the game).
The best thing about UO was how real the game was. Far more life-like than any other MMORPG I've ever seen and it came out in the 90's.
I only played UO for a month or two. The only skill I leveled up significantly was Hiding. I'd go where the loot was, and adventure for a few minutes until the inevitable gang of PKers came wandering through, looking to loot all the players like me. Some players ran, some hid, most died.
If you successfully hid, your player would be invisible to everyone else. So the PKers would walk a pattern through the dungeon, trying to step on every square. As a cowardly hiding level 1 character, I'd wait in hiding as long as I could, then jump out of hiding when I saw a chance to escape. Invariably I'd be spotted. I'd run around a corner, hide again, and the process would restart. I swear I spent more time hiding behind rocks than fighting whatever monsters the game made available to low level players. I could never tell if I was having fun or not!
Reminds me a little bit of REAMDE.
> The only skill I leveled up significantly was Hiding. I'd go where the loot was, and adventure for a few minutes until the inevitable gang of PKers came wandering through, looking to loot all the players like me. Some players ran, some hid, most died.
Really expected your story to be focused on scavenging the loot the PKers left behind.
I can't imagine how the UO devs thought this might be a turnoff for new players.