As far as a home on Ft. Salonga Road in Northport - commercial development in the area may have an impact on the pricing, depending on where it is. Also, there's a seasonal factor as the traffic, folliage, etc. changes and homes become more or less appealing based on those seasonal factors.
Local real estate agent is your best resource, period. Zillow and other sites like it can't possibly provide accurate numbers or analysis of home values. Real estate is local. Always has been - always will, no matter what technology they come up with. A website based in California, can't possibly help you learn about a market in NY. Ever. Their numbers are dated, based on (in some cases) tax values!!!!
I mean, you're in Nesconset and you're using zestimate online? Remember, you don't pay anything extra to a buyers agent. Our fee is built into the closing costs. So you determine the price you want to pay and the seller pays all Real Estate Fees. If you enter into a situation where your agent, who's representing you as a Buyer, tries to tell you that you need to pay any portion of the real estate fees above and beyond the sales price - doesn't know what they're doing. Move on.
Overall - I would strongly recommend that you pay no more attention to websites that provide "estimates" of values.
There is truth is both answers. A "Realtor's" code of conduct and ethics dictates, when representing a buyer, to "form fit" their personal criteria in to a reality. Simply put, best location and price for the area you are searching for! Data is totally meaningless unless the heart is invovled. Purchasing the perfect home is all about your emotional and financial commitment.
The Long Island market is growing in some specific areas, and still on a downward trend in others. The signifance is that we have seen drops from as low as 7% to as high as 20%, on average, based on the truism of supply and demand for a specific location, and of course condition of the home!