Some buyers have a misconception that in a buyer's market, low-ball offers are the way to negotiate a sale.

Ultimately, a house will sell for the market value. Therefore, looking at a listing price and automatically deciding to knock 20% off, thinking the seller is desperate to sell, is not a sure-fire way to write a successful offer.

Feeling out the reason behind the sale is key. If it's an REO, obviously the bank is selling the house to offset a loss. A short sale isn't a far cry from that. A traditional sale is the most flexible. Any number of reasons can be involved, so have your agent inquire about the seller's circumstances and motivation level.