it would be helpful to know the source from which such an estimate originated.
If you are using aggregate websites you will need to read all of the explanation regarding how they derive at this calculation. Your conclusion will be these aggregate websites are inadequate in providing actionable data.
You may have used a service such as House Values and requested a market analysis. The agent preparing your report did not visit your home so has no knowledge of the condition, updates, additions or other aspects that may add value or detract from your home value. However, the agent DID prepare the estimate using comparable properties that conform to the data YOU PROVIDED and the agent will have used only recent, non-distressed sales.
Even with the greater accuracy, the range will be reflective of the market value range of your community. If one home sold for $250K and another nearby home sold for $550 of similar size and age as yours, you can see how a home visit can bring more clarity to establishing the home's potential selling price.
You might just as well do what you have known you need to do, pick up the phone and call one of the Galloway NJ real estate pros.