The seven costly mistakes
Mistake 1: Putting the home on the market before it's ready. Most times this happens because the seller gets impatient or is a procrastinator and has pushed himself up against a moving deadline without getting the pre-sale work done. So it comes on the market with the horrible carpet (that gets replaced during the marketing of the home); or they are painting it while it goes on the market. Presentation is everything -- so get the work done before marketing the property.
Mistake 2: Over improving the home for the neighborhood. This happens with additions, bump outs, and upgrades that make the home stick out from among its competitors so much that it's an anomaly, instead of a nice addition to the community.
Mistake 3: Pricing the home based on what the seller wants to net. This pricing strategy always ends in failure. Sellers can control the "asking" price, but they don't control the "sales" price. The market does. It doesn't matter what the seller wants, the price is determined by the black-and-white, matter-of-fact reality of the market.
Mistake 4: Hiring an agent based on non-business factors. Make sure you're hiring a professional with a proven track record. It might be nice to hand over your largest asset to your nephew who just got his license -- but make sure he has a mentor to keep your deal from going south.
Mistake 5: Getting emotionally involved in the sale of the home. This is one of the biggest challenges home sellers face when putting their house on the market. Once you decide to sell your house, it's no longer a home, but a commodity. It needs to be prepared as a commodity, marketed as a commodity, and priced as a commodity. It doesn't matter what you "want," only what the market can bear on pricing. People are going to come in to kick the tires, so to speak, and you can't get emotional about how they may or may not appreciate the nuances of your home of seven years.
Mistake 6: Trying to cover up problems, or not disclosing them. Most states have a property disclosure/disclaimer form -- use it wisely. Just because you disclaim doesn't mean you cannot be sued later for the leaky basement, or dilapidated heating/air system that's discovered 30 days after settlement.
Mistake 7: Not getting your ducks lined up before trying to sell. This would involve financing, reading the fine print on your current mortgage to ensure no pre-payment penalties, not listening to the particulars of your local market, etc. If your local market is dictating lower home prices, then lower it early, not later -- it will cost you more. If the local market dictates selling your home first, then buying second, do it in that order, or vice versa.
Avoiding these mistakes is not that difficult. There are plenty of resources (like this publication) and professionals, who are there to help you step over the pitfalls. Do the research early, and listen to that voice in your head (it's probably the whispers of the finance, real estate, insurance person who's warning you of a hole you're about to step into).