I'm with Hypnotoad on this one, it cloggs up the forums and is unfair to other sellers. I dont personally use the 'Plug' threads, but i do read them and have a nosey at the auctions, but even i'm getting a little annoyed that the same items are reappearing.....
If you are selling more then 1 'subject' of items then there is nothing stopping you from putting a little description above/below the links. Again, its unfair for the sellers who only have 1 shop.... and so can only advertise 1 shop. Why should the rules be changed because some sellers have more stores then others?