In some forums I've known, you need to gain  + trust in order to remove the negative trust. just like mathematics:) but I guess is isn't removable in this forums, 1 mistake can ruin all your deeds.

why would you ask for merits? to join campaigns?
don't just ask for merits, work hard for it, just like as other says QUALITY POSTS to gain merits. if its just as easy as asking, how will the managers know if you're capable of joining their campaigns? If you're brilliant enough to posts informative threads or whatever campaigns do?. there is no such thing as shortcut, learn the basics, learn more to gain more. I'm just a newbie, I think I'm in no position to answer your question, since you are higher than me, but I guess it helps.