I would agree if posting an action was somehow a rush thing where you need to put an item and the price in within seconds and click ok or it wouldn't work. As it is now, you have all the time in the world to review what you are posting and what price you put in, before you click ok. What would an extra 30 seconds do? If you didn't check what you put in at posting, why would you check after posting?
I'm sorry you lost your auction to a sniper (which, as everyone else has said, is not a bot), but that's life. You could try to contact them and kindly ask the item back or offer to split the difference. Most snipers don't pray on people who make an honest mistake, but on people who simply don't know or don't care about the real value of an item.