Fee to sell a house is something one comes up with the agent. This percent will change depending on each agent and is will vary according to services rendered. As a rule of thumb, you can think about 6%, going up and down from this number depending on agent, issues, amount of services wanted. There is NO hard and fast number.
If one is a buyer, then the fee is nothing or something depending on what you need as buyer. Normally, in a MLS situation, the buyers agent is given a cut of the selling agents fee, and the buyer will pay nothing to little to have an agent help them - but again its a issue you will work out with the agent.