After much thought, I agree that the cons outwiegh the pros of this, in much the same way that congress has a way of outweighing progress. Trades are, and will be a part of HLP. A labor trade forum for things not readily available would be good.
First thing, no asking for finished assets. That is just poor form.
Second point, do not get specific in the post about needs, save it for PM or whatever, but keep needs private. This would stop some of the aspects of hoarding, as it isn't readily available that fredder X is looking for a model of Y and is willing to build Z number of missions.
Third, the requester should post what skills he/she is bringing to the bargaining table. This allows anyone looking at the post to see if the requester can provide them with needed labor. It would actually help to get a response. Just keep it brief. I can fred, do some pof work, and table hack is a good example. Don't be specific about what mods you have worked with, save it for PM.
Four, don't post what you think someone else's labor is worth. ie would be willing to fred x number of missions, or pof y number of models...etc etc.
I think that would alleviate some of the problems that I hadn't thought about, and that others brought up.