Remember, you are not an expert. If your valuation leads you to believe that a particular home is undervalued, you should get a second opinion before making a decision to purchase that home. An immediate option is to use real estate broker to help you assess value of the home.
However, the valuations of brokers are sometimes intended to serve the seller rather than the buyer. That is why they may overestimate, or underestimate the value according to the context and the employer of their services. In this way, the brokers can ensure that a home will sell at a higher/lower price to serve their purpose, which is to gain a brokerage fee or commission. Therefore, irrespective of the honesty of many real estate brokers, you should always conduct your own simple valuation to guide you throughout the purchase process of your home.