An individually performed Comparative Market Analysis is the "gold standard" for approximating market value - period. A Comparative Market Analysis (CMA) gives you the best representation of market price/activity/trend direction - for the specific property details you search on. Just because a property sells right next door to another does not mean that it's a comparative match. Days on Market (DOM) for the properties that have sold contained within the CMA is another clue of "market velocity" that help determine offer price.
My suggestion: Interview a few Realtors, pick one, and then team to develop a purchase strategy based on what sector of the market you are interested in.