1. Boxing isn't hard, but it's not easy either. I don't see farmers being able to box instances. I've seen some who have a hard enough time killing non-elites their own level, and most look like they only use 2 or 3 buttons tops.
2. Botting is easier. Doesn't require any manpower.
3. As zanthor said, 5-boxing = 5 banned accounts. It would be a huge red flag if a priest+4mage group did nothing but farm instances and mail gold. With a single character it's a lot easier to fly under the radar.


More than gold farming, I think selling characters would be a bigger concern. Get a 70 frost mage and 5-box with 4 alts from 1-60 in a few days. Not sure how long it takes to "order" a level 70, but boxing would dramatically reduce the time.