Me too, I managed to get a dozen of mispriced materia before. It clearly show that people blindly undercut others, it went like this :

1100 -> 5-6 on the list by retainer A
1200 -> one from retainer B, tried to undercut retainer C but missing a zero
12500 -> retainer C

I don't camp the board for this, I always have something to sell everyday so when there's a misprice for the item I'm trying to sell I will rush to the board to buy it off and resell them. I just hope they don't get frustrated over their own mistake.