[...] one of legendary staff members started promoting obvious ponzi with avatar/personal text [...]
You cannot expect staff to judge whether or not a specific service with a referral scheme is legit or not.
So there's only two possible solutions to the dilemma of staff sometimes accidentally (or willingly) promoting scam:
1. forbid advertising for staff
2. let them do whatever they like
I personally would opt for 1.
I think it is pretty clear that in this case the site that is being advertised is a scam. That is the major difference, sure someone could get duped into advertising what turns out to be a scam, however the evidence is clear.
I think that anyone who advertised such a obvious scam is someone whose word should not be trusted, and is not reputable and the forum staff, and more importantly, the people on level 1 default trust who be trusted and should be reputable.