3. Not backing up your price--There's an art to presenting an offer that's substantially under the asking price. A low offer could start negotiations off on the wrong foot if you're not careful. The key is for you or your agent to explain the offer when presented. Sellers want to know why you're coming in so low. Include recent comparable sales in the area or issues with the property that validate why your offer is so low. Don't be too harsh with your criticism, however, that can also work against you.

4. Not knowing what you're willing to pay--Buyers these days have a strong motivation to get the best possible price on a property, especially if they believe that home values will fall even more. But sellers have limits, too, most often dictated by the amount of home equity they have. Before negotiations begin, it's important for a buyer to decide what your walk-away price is. While a buyer should know how high she is willing to go, don't put limits in the first offer. You lose integrity if you say it's your best and final offer, but then are willing to come up with a few thousand dollars more in order to buy the property.

5. Not making a clean and easy offer--When you make a low bid, you want other elements of the offer to be attractive to the seller. And a deal that can close quickly often will have appeal. Make sure there are as few contingencies as possible. It's best if buyers don't have a home to sell in order to buy the one they're bidding on. Also, have your financials in order from the start. Loan qualification is more difficult these days, so it's important to have a lender pre-approval letter.

6. Assuming cash will always get you the best deal--Cash is king, but in the end, a seller often wants the most money for his home regardless of if the buyer needs a mortgage or not. So don't think making an all-cash bid will automatically mean an accepted offer. That said, if the seller is a bank because the property is a foreclosure, the institution may accept a lower offer from a cash buyer, as opposed to someone who needs a mortgage. Banks often don't want to deal with mortgage-related delays.