Like any other business in the history of business, your broker’s raison d’etre, is to make as big a profit as possible. There are about as many ways to go about this as there are brokers. For those who are in it for the long haul, however, it is generally best to adopt a set of practices which are deemed fair by their clients: certain boundaries are set, and operating beyond them can cost a brokerage its reputation, and along with it its clients.
Straying outside these boundaries, therefore, is not considered as being in line with the long term goals of the business. How strictly these boundaries are enforced, especially when there is little chance of clients ever even becoming aware of any transgression, again varies from business to business.