Can an appraiser use sales that are not in MLS?
Although the Multiple Listing Service (MLS) is the primary research tool used by appraisers in Palm Beach County, the use of sales that are not in MLS in an appraisal can be perfectly acceptable. The main reason appraisers use MLS is because they need to confirm the terms of sale for the comparable.
Examples of terms of sale that are available in MLS include whether the home was purchased with cash or financed, whether there were seller concessions, whether the sale was an arm's length transaction, how long it was on the market, etc. The MLS also will also typically have photos, the contact phone numbers for the listing agent and selling agent, and comments about the home.
If you want an appraiser to use a non-MLS sale as a comparable, then you may want to try to obtain sources for this information for the appraiser. The appraiser is only in the neighborhood during the time of their inspection, but you probably live there. If a neighbor's house sold and you can find out the new owner's phone number, that would be a great start.