IMHO an auction, by definition, is a free-for-all. Whether it be an estate auction, public auction house, or fantasy baseball. I couldn't fathom an auction where you had to go in turn.
I don't like the flag thing either. Wouldn't want to telegraph my intentions to the other participants. Sometimes I bid early, sometimes late. Sometimes I bid in the beginning, then drop out only to jump in again at the end. Keep them guessing.
For us, order is determined by throwing a pen into the middle and whoever it points at nominates first then proceed clockwise.