Ask friends, family and anyone else that you know whom they have worked with in the past and what their experience was. Referrals are a great way to find out information on which companies are performing well in your area and which aren't. Find out how long it took to sell the property, if the agent they worked with was professional as well as accessible and if the property sold for the expected price, more, or less. Google search the top agents in your area and spend some time researching the results. Find out which agency has the most listings, look up profiles of local agents and the company's that they represent and see who has the most effective listings for their clients.