Most stock brokers charge fees for trading stocks and some of them charge like $7-9 per trade. Why do they charge fees? Do they need to pay fees with stock exchanges like nasdaq when shares are traded or is it to make more profit for the brokerage firm?
They are providing you a service and they charge you for it. The service includes giving you a trading platform(website and the infrastructure), doing all the background work for setting up services for you, relaying your orders to the market or as a broker fulfilling your orders, doing settlement when an order is matched, giving you access to the stock market(the costs are quite high to get a license to relay orders to the market and I believe it needs to be renewed every year). There are transaction fees which the stock exchanges charge the brokers to use the stock markets infrastructure and connect to it. And then interfacing with banks for monetary transactions and also doing according to the law in the jurisdiction they are located in.
Most of it is an one time cost, but they are a private enterprise out to make profit so they will charge for their services.
Retail brokers and are generally not members of exchanges and would generally not be members of exchanges unless they are directly routing orders to those exchanges. Most retail brokers charging $7 are considered discount brokers and such brokers route order to Market Makers (who are members of the exchanges). All brokers and market makers must be members of FINRA and must pay FINRA registration and licensing fees. Discount brokers also have operational costs which include the cost of their facilities, technology, clearing fees, regulation and human capital. Market makers will have the same costs but the cost of technology is probably much higher. Discount brokers will also have market data fees which they will have to pay to the exchanges for the right to show customer real time quotes. Some of their fees can be offset through payment for order flow (POF) where market makers pay routing brokers a small fee for sending orders to them for execution. The practice of POF has actually allowed retail brokers to keep their costs lower but to to shrinking margins and spread market makers POF has significantly declined over the years. Markets makers generally do not pass along Exchange access fees which are capped at $.003 (not .0035) to routing brokers. Also note that The SEC and FINRA charges transactions fees. SEC fee for sales are generally passed along to customers and noted on trade confirms. FINRA TAF is born by the market makers and often subtracted from POF paid to routing firms.
Other (full service brokers) charging higher commissions are charging for the added value of their brokers providing advice and expertise in helping investors with investment strategies. They will generally also have the same fees associated with membership of all the exchanges as they are also market makers subject to some of the list of cost mentioned above. One point of note is that Market Making technology is quite sophisticates and very expensive. It has driven most of wholesale market makers of the 90s into consolidation. Retail routing firm's save a significant amount of money for not having to operate such a system (as well as worry about the regulatory headaches associated with running such a system). This allows them to provide much lower commissions that the (full service) or bulge bracket brokers.