if it's at $990 and you put a buy order at $1,000.. doesn't it automatically buy at that price, or do you need to confirm when BTC hits 1k? couldn't the walls be prevented if you are forced to buy at the price point of your order?
for a professional trader it's all about getting the best price you can, buying or selling.
So if the current price is $990, you don't put in an order at $1,000 of course.
You put in an order for say $900, and try and move the action down towards your bid.
You can do this by putting a "sell wall" (with no intention of actually selling).
Sellers behind that wall will get no bids unless they jump the wall (lower their offer price) hence moving them towards your lower bid price.
It's mostly psychological, but it works, as most newbs can't work out what is going on...
the way to overcome them, if you have the money and the stones, is to take out their wall in one hit, before they can move it.
annoys the shit out of them, loses them money and makes them think twice about doing it in future.
The games that go on...