Being an appraiser, and/or broker requires training in many aspects of real estate. Not the least of which is finding market value. However, more often than not, these two professionals will find different values for the same property. Why? The most common answer is that they approach finding value differently, even though they may be looking at the same raw data.
The broker has an eye more toward future prices (what they can sell the home for, within a few weeks). The appraiser bases most of their analysis on closed sales. Which means in a very volatile market, values could be changing so rapidly that between the opening and closing of escrow (21-45 days) the values have changes 1 to 5%. Therefore, once the sale closes it may already be considered old.
So, which report is more accurate and gives you a true value? Answer: a combination of both. If you are buying or selling, have an appraiser give you a present value and a value as of 30 days in the future. This may cost you a little money now, but save you big in the future. Remember that appraisers have but one job: finding value; they have no future interest in the property.