This is a common nickname, which is sometimes awarded to croupiers in offline establishments.
Killer – dealer, which constantly wins have a certain groups customers or have majority visitors in a whole.
This the dealer does not want to see at his table most of the experienced visitors. They ask them to change or go to another place.
On the other hand, there is a category of customers who understand that no dealer will always be lucky. They are often even happy to play with such a croupier because they are sure that soon fortune will turn away from him, and he will "be generous" with large payments.
Practice shows that there are cases when the dealer, who was a "merciless killer" all shift, at the end of one approach gives customers all the proceeds of the casino.