BEND, Ore. (CNN/Money) – To say that it's been a seller's housing market is the understatement of the year.

Homeowners looking to sell in most parts of the country haven't had to wait around very long for a suitable offer, and those in the best markets have seen their homes swooped up in a matter of days, even hours.

In early 2003, in fact, 21 percent of all houses went into contract less than one week after going on the market, according to the National Association of Realtors (NAR). On average, houses sold in just five weeks – nearly half the time it took throughout the 1990s.

"I believe this may be our best year ever," said David Hemenway, a realtor in Cottage Grove, Ore., who's been in the business since 1968. On the other side of the country in Sebring, Fla., realtor Chip Boring is enjoying a record year.

Yet, both are aware that great times can't last forever. "Up until the last 2 1/2 years the average time on the market was anywhere from 180 days to 210 days," Boring said. And Hemenway recalls the early 1980s when his listings lingered on the market, sometimes for years.

As interest rates creep up, buyers' budgets creep down and markets return to more normal levels, sellers will discover that it takes a little more work (and patience) to unload their homes.

Many already have.

While there is little you can do to change the laws of supply and demand, you have some control over whether your house sits or sells.

Here are the most common reasons houses don't sell, in order of importance.

Even in the best of markets, setting your price too high is a mistake -- unless you really don't want to sell your house.

"Starting too high is the worst thing you can do," said Hemenway.

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Why? Because your greatest opportunity for selling your house is immediately after it goes on the market. That's when the majority of serious buyers will see the house.

"Even if you lower the price to reflect the market, you'll have fewer people coming through than if you'd just priced it right to begin with," said Hemenway.

In fact, it's not until after you bring the price down below the market – something few sellers want to do – that interest will pick up again.

To make matters worse, say real estate agents, the longer a house sits the harder it is to sell. "Everyone thinks there must be something wrong with the house if it hasn't sold," said Boring, adding that for this reason he won't take on a listing if the seller insists on asking more than the house is worth.

To drum up new interest among buyers, sellers sometimes pay for extra advertising or offer to, for example, pay for closing costs as a way to get buyers' attention. "In markets where people don't have a lot of cash, paying for closing costs or buying down interest rates with points up front can put you at a huge advantage," said Ron Phipps, a realtor in Warwick, R.I.

When markets are good, buyers are more willing to buy on the outskirts of an area or turn a blind eye to busy streets, bad views and other problems. But when markets cool down, it's these spots that suffer the most, said Hemenway.

Short of moving the house, there is not much you can do if it is in the wrong location. But while in the house you can take care to make sure you don't over-improve your property relative to the ones around it.

"If you have a $300,000 house in a neighborhood of $100,000, be prepared to lower the price or let it sit," said Boring.

Realtors say that getting buyers to take a look inside a house is the biggest challenge of selling a house. Once they've stepped through the door buyers are more likely to consider a place.

"I recently sold a house that from the front was not very inspired," said Phipps. "The buyers came to the open house only because they needed to kill time, but once inside they were interested."

For this reason, a little time and money spent on curb appeal will go a long way. Trimming the grass, washing the windows and planting a few flowers may be all it takes.

In the case of houses whose best features are inside or out back, Phipps recommends taking good interior pictures and putting 360-degree tours online.

Sellers sometimes get buyers to look past their homes' imperfections with creative extras. "I've seen sellers offer decorating allowances, and pay for cleaning service and landscaping," said Phipps. "Several years ago a seller in the bakery business offered to bring the buyer a different cake every month."

Less is more when it comes to attracting buyers.

"Put all of those pictures of your family and other personal treasures away," said Sheryl Gregory, a broker in Wynthrop, Maine. "It distracts buyers and makes it harder for them to picture themselves in the house."

She also recommends taking down distracting curtains and putting on a fresh coat of paint. "Buyers sometimes get scared if they wander through a house and think they're going to have to do a lot of painting," she added.