More to the point, airlines and travel agents once enjoyed a symbiotic relationship. What benefitted one benefitted both. Besides the obvious (commissions), agents referred friends and clients to airlines they preferred, and even received year-end bonuses from airlines based on booking levels and the like.

Had this fare been posted on Worldspan or Amadeus 15 years ago, I daresay BA's corporate HQ would have been deluged with phone calls from TA's pointing out the error within the first few minutes of its posting. In the interim, how many people would have successfully booked such a fare? Maybe a handful. As you mentioned, the agents would likely have had little interest in doing all that work for so little commission.

Well, the airlines don't want the TA's anymore ... now they're marketing fares to the public, who have absolutely no vested interest in the airlines' well being. So things like this will happen, and will be exploited to the fullest extent possible.

The phrase cutting off one's nose to spite one's face jumps to mind.

Mook