Asked on 18 Jun 2018
As part of the order that you put with your broker - there would be some price guidance (eg buy 5000 at $1.10)
if there is only limited liquidity at that price (eg seller offering 400 at $1.10) then your order is partially filled (the broker got the 400 for you) and your order is queued in the outstanding order book of the exchange for filling when other sellers come.
Depending on what is the rules at your broker, the order can hang around waiting for a while (eg until market close) before being canceled. Once canceled you get as much as filled and order is considered done.
This means that your order was partial filled.
You wanted 5000 but the broker was only able to match you with a seller for 400. So, you managed to only buy 400.
This means that you still have to pay the FULL commission on that 400. This also means that the stock you want to buy is very low in liquidity.
A suggestion for low liquidity stock and to save on commission is to buy from the "ASK" queue rather than wait for the "BID". The spread between the ask and bid would likely be quite big but at least you dont run the risk that you waste commissions.