There is a huge buyer fear in overpaying for a property. There are a number of different ways to ensure that such does not happen. In truth, it's very difficult to overpay for a property.

The best way to ensure that you do not overpay for a property is to have an agent that is very well skilled in calculating property value prepare a Comparable Market Analysis, also called a CMA.  A good CMA should include a detailed spreadsheet such as this which compares various homes and adjusts their values based on the differing features.  Some CMAs are very long, mostly computer-generated and have some value.  Of more value is a CMA that has an adjustment spreadsheet, as shown here.

There are a number of services that real estate agents use that will automatically generate these reports, and they are usually quite long.  These computer-generated long reports are not particularly useful as they are very high on page volume, but very low on detail. It is best if you see a CMA that has been calculated and shows how the value is arrived at.

Something else that prevents overpaying is the lender. The lender will send an appraiser out to the property who will evaluate the home in person and create something very similar to the spreadsheet previously shown. Different parties have different viewpoints on the value of a home, and there is no value that is definitive with the exception of what buyers are willing to pay for a home. The seller, the buyer, the real estate agent, the appraiser, and the assessor will all have different value numbers for a specific home. What really matters is the price that the market will bear for the home. 

Ensure that your real estate agent develops a detailed CMA.  That will be closer to the real market value as your agent is more familiar with the market that almost anyone else.  In the end, if you have a good real estate agent, you will not be overpaying for your property.