When a "deal" of a property comes onto the market it will go under contract quick. Yes, even in today's market, the properties that are under valued for that particular area it very well may sell over the listed price. So it is very important to work with a Realtor that keeps you up to date on the new listings that come to the market. One tool that some realtors use is an automatic email service that is offered through the MLS.
It must be frustrating to buyers calling on properties at always seem like there pending by the time they see them. In this area it's actually the cost of the seller to pay the entire real estate commission. That means that you as the buyer can "hire" any realtor and make them work for you for free!!! The question then becomes how do you choice the right realtor for you. One quick read to help would be at the National Real Estate site.