Let me inform you that there's no system that could avoid bad users, you have to moderate on your own and ban anyone doing stuff like that.
There is no system? Sorry but i just give you solution to you disable option for registered users to they can't change the title. Not need to ban user in this case, if that option is disabled, then user can't change title,and then ads are safe.
I won't touch one single line to get your purchase because we have a structured way to get features added to the system
Is not here if i purchase, and is not to you doing that only for me.That you doing to all your customers,if someone send you reasonable solution,which is my in this case,you will change that.But i can't push you to do that,this is your project,i just want to give you idea,which is not hard to change that single line.
P.S. I can't now if i have example 54,944 posts and in which one user has change title to illegal word.And if i found that word, will be late.