The LFMs never bother me. It is a player response to a needed feature. There are never more than a few up at a time. I recognize that they are against the rules.
Here's a solution - devs add level 0 to the window. Require LFMs to be posted as Level 0. Have default not display level 0. Don't want to see it? No problem. Want to post? No problem.
I would never report someone as harassment for the LFMs as long as they don't spam/PM, but that's just me.
The trade forums are not a very efficient way to trade. It is outside of the game. It can take several rounds of e-mails to get a deal agreed to. Then you need to meet up with the person, sometimes taking days or a week later.