When looking to sell a house, most people start by talking to their local estate agent – this has the advantage of using their knowledge, experience and contacts in a particular area to market your home, additionally estate agents advertise regularly and have marketing systems in place.
The disadvantage with agents can be their fees, the large volume of houses they're dealing with and not being able to guage how pro-active they are with your property.
Before you settle on an agent, talk to a few in your area – ask them all what they'd like to list your house at, what price they think you'll get, and how long it will take to achieve the result. The more you speak to the better idea you're going to have of what is actually achievable, and you're going to know whether one agent is inflating the price to get your business, or buttering you up for a low offer from one of their friends.
Look for an agent that is regularly active in your area, sometimes the biggest agent in town may not be the one that's best for you, because they don't focus on the area you're trying to sell in. Consider the smaller agencies that have a better knowledge of the area you live in.
Ask all prospective agents whether they keep a list of people looking for property, a good agent should have a system in place to match enquiries they get from buyers with properties for sale – ask them up-front whether thay have anyone on their books looking for a house like yours.
Most importantly, even though you're paying them to take away the hassle of selling your property, make sure you hassle them so that your property selling remains their priority!