I have been noticed many same players selling various items in steam market and I know that they are bots. They are used for buy under priced items and sell them back to market for profit. It is against rules using bot in market?
EDIT: I did find out how to spot them easily. You do this: Buy Vintage Pyrovision Goggles from market then resell it to market for lowest price possible. Then it will buy market bot within seconds and on "My Market History" you can see who bought it. Go to his profile and report him being bot in market. It costs 4 cents per report(with euros).