I think no advertising on cross-realm, and only by an individual actively participating in the sale, are both pretty clear. If you are going to advertise the sale, you need to be participating in the run. Not your alt, but the toon you advertise the sale on.
Edit: if you are just part of the run that someone else, who is also in the group, advertised the sale on, that is fine. it is the toon who advertised the sale that HAS to be in the group.