Don't rely on the real-estate agent to tell you what to do. Even the most wonderful agent isn't exactly motivated to get you the cheapest price. Remember, unless your agent is specifically a buyer's broker or buyer's agent, she will typically be paid a commission—based on a percentage of the sale price—out of the seller's pocket. If an agent helps you to negotiate a lower price, her commission will be lower, too.
So, before you begin shopping, scour the Internet and the local paper's real-estate section. Pay attention to homes in your range; don't track million-dollar manses if you'll be shopping for a $200,000 condo. For at least six weeks, keep a record of how long sold homes were on the market, and whether they sold above or below the asking price and by how much.