The key in negotiating a lower sales price in a depressed market is the expertise of the Realtor that you have representing you;
1. Be sure they specialize (thus know the market) in the area that you are purchasing in.
2. Be sure they are detailed oriented and can do a detailed market analysis on the area, and will back up your offer with statistics.
3. Be sure, they are a Certified in Negotiations
4. Choose someone that you Trust and have good rapport with.
It's important who you choose to represent you. I would interview at least 3 Top Agents who have a stellar business.