Do you realise how big your big your wall would get? Would get to hard to find allies. Spam all over the wall... No support.
Generally, a decent idea. However, like Flames stated... Your wall will eventually be spammed to the point that no one will be able to find a decent Allie and you can only see so many posts. Nice try though.
It doesn't work no one bought my ally from your wall..... And I'm sure smart ally traders can do there own research to figure out if they want to hire or not