A full time agent is preferable because of constantly changes trends in the marketplace. You can also check with the state licensing agency if you're not certain of an agent's certification. Work with one whose license is in good standing.
Brokers have more stringent licensing requirements and responsibilities.
Other home sellers will want an agent that understands their concerns, is business savvy and a creative marketer. The more exposure your home gets, the better. An agent who knows the area or neighborhood you are interested in is extremely beneficial to you. You want an agent who will give you personalized attention, answer your calls quickly and communicate with you often. Keep in mind, though, many busy, experienced agents are the most efficient.