Local real estate brokers will have good comparable sales data, and you can also find useful information online.

Whether the local real estate market is hot (prices are going up) or cold (prices are dropping). In competitive areas, you'll have to offer the asking price or more, and expect bidding wars to erupt among frenzied buyers. Homes often sell for 10%, 30%, or more above the asking price in hot markets.

You'll want to arrive at a bid amount that will beat out the competition -- but only just. Some buyers, however, deliberately bid sky-high in order to stop the madness and find a home as soon as possible, especially if they have been outbid on properties two or three times already.

In a cold market, you'll have more room to negotiate with the seller, and you may get a bargain.

The seller's needs. Remember that price alone is not the only consideration for sellers. Your ability to close the deal quickly -- for example, by having your loan preapproved, or by not including a contingency saying that you have to sell your existing house first -- is often crucial, especially in hot markets. Finally, your flexibility and sensitivity to the seller's needs -- whether it's extending the closing date for a seller who can't move for a few months or making the offer "as is," meaning that you pay for needed repairs -- may make or break your offer.