Hi Paintman I'm not an expert but I believe the large...

Hi Paintman
I'm not an expert but I believe the large institutions and brokers use a completely different platform from us retailers. Rather than put in an order for a parcel at a certain price, they can program a robot to place/execute small orders throughout the day, and then charge brokerage on the total amount (not on each tiny trade). This might come in handy say if someone had a large parcel to sell (or wanted to accumulate a large parcel). By buying/selling shares say every 10 minutes they are guaranteed to have either bought or sold at the VWAP (volume weighted average price) for the day, and they haven't pushed the market up or down by dumping/buying in one hit. Hope this makes sense.