Why not use the forum's self moderation feature if the goal is to prevent others from posting? The self moderation feature is dedicated for such a thing and even gives other users viewing the thread a warning whereas lock-posting can be used to deceive, especially provided that there's no public log or warning. Especially for past activity that could be completely fabricated in a thread with this technique.
That would probably be ideal, though its their own choice I suppose. Some people don't know how to use the self moderation feature, I guess some people just don't want to bother moderating people's posts in the first place, so they decide to just lock their threads to keep replies out. If someone is doing something they shouldn't be doing, and you can't post directly in their thread, you just make a new thread yourself.
I don't really see how bump and locking one's own thread is any worse than self moderation. If someone's intentions are to deceive, they are going to do it one way or another, don't be fooled, leave them feedback on their trust page, or create a thread to let people know.
