I agree that it would stop you from trading a bot but, /busy does not always indicate a bot. I run w/ /busy all the time even in dungeons. I was getting spammed 20-30 times a day. I was filling up my black list every 1-2 weeks it was getting insane. So since they would never get rid of the spammers I put /busy.
Saying /busy is a bot is like saying a specific race of people are always criminals. I just do not pay attention to them any more it's not worth my time.