There's a disruptive force at work in Westport and Weston real estate.

No, it's not high inventory. It's not foreclosures or short sales. It's agents from other towns -- who know little or nothing about the nuances of our local markets -- representing our buyers and sellers.

It seems obvious that this is not a good idea. If you're about to make one of the largest financial transactions of your life, why would you put your fortune into the hands of someone who does not have the expertise to advise you properly? Most people would not be so cavalier in choosing a plumber or even someone to cut their lawn.

Yet every year, a smattering of local homes for sale sport signs with the names of brokers with whom none of us are familiar. And I receive calls to show my listings from agents based as far away as Milford and Danbury.

For sellers, choosing a non-local listing agent is often the result of a misplaced sense of loyalty. You may feel indebted to Betty from the garden club, who sells in Darien and has been working on you for years to list your house with her. And then there's your niece Sue, who sells in Trumbull. Of course you want to give her a try.

For buyers it's usually a matter of ignorance. Most who work with out-of-town agents are first timers who don't know any better, or are out-of-towners themselves who come from places where agents cover a broad geographic territory. So working with a Stamford agent in Westport or Weston may not seem unusual to them.

The problem is, Betty and Sue and the agent from Stamford are not local experts. They don't know that the YMCA is moving, or where the school bus traffic snarls occur every morning. They don't know when wetland regulations are about to change, or that a town-wide property revaluation is taking place that makes the tax numbers on the listing sheet meaningless. They don't know which transitional neighborhoods in Westport are safe to invest in. They don't know where the power lines course through Weston.

Just as I would not know these things about Darien or Trumbull or Stamford.

The difference is, I would never be comfortable guiding buyers or sellers in these towns. When someone asks me to represent them outside my area of geographic expertise, I do what any trustworthy agent would do -- refer them to an agent in that town who knows as much as I do here or partner with a local agent there who can fill the gaps in my knowledge.

Many in my line of work argue that you don't have to be an expert in a given town to sell a house there. And I suppose there's truth to this, since it's not that hard to access MLS stats for another town and get a gross understanding of what four-bedroom colonials there are trading for. So then why is it that Westport and Weston homes listed by out-of-town agents are usually priced too high and expire without producing a sale more often than properties listed by local agents? And why do Westport/Weston agents love it when out-of-town agents show our listings? It's because their clients tend to make deals at numbers higher than a locally-represented buyer would pay. Those in my business see this happen time after time.

So I counsel local buyers and sellers to beware the out-of-town agent. And I implore my non-local colleagues to think twice before attempting to sell someone something you don't know very much about, as it's not in your client's best interest.

Evi Coghlan's "The Real Deal" appears every other Friday. She is a licensed real estate agent with the Riverside Avenue office of Coldwell Banker and a former marketing consultant to Fortune 100 companies. She may be reached at 203-247-6691, by emailing her at evi@evicoghlan.com, or visiting www.evicoghlan.com.