There's a lot of threads in general about how such seller is so good, this one so bad, etc.
How about a new forum to centralise that kind of information ?
Name could be "Sales feedback" or anything more appropriate - not a native english speaker here.
Not sure where to place it, maybe stay in the "general" area so that it's easily located by newcomers wanting to decide what they will buy. Or else put it in the marketplace section.
Also, if it is decided to create it, should the existing threads be moved there (if that's possible) ?