I think that there is a clear difference between DT1 and all other levels of the DT system, because it is more than clear that my feedback does not have the same weight as the identical feedback of one of the respectable DT1 members. Their lack of interest (with some exceptions, of course) first of all encourages sellers and buyers, and creates an image of some kind of situation that can be defined as "I don't really care about it"
While I do agree that feedback of some members has more weight (and some less due their tendency to leave all sorts of questionable feedbacks) I don't think that it has to do with DT1/DT2 status but rather with reputation of those members.
I honestly don't see how its different if account seller gets tagged by a DT1 member or DT2 member and would really like to see the example of what you are talking about. I mean, since account sale is not forbidden by forum rules, all we can do is tag them and then its up to them to decide whether they will continue selling or not.