Laurie: There are several things that can be done by both the Realtor and the seller. The Realtor can insure that the appraiser has all relative comparables and sales explanations prepared for the appraiser, and can meet him or her at the property to point out its features. The sellers can make or keep their home as presentable as possible, as appraisers will also be noting the condition of the property. These are suggestions most Realtors will offer to their clients.
In Addition, I like to review the comps and pending sales before the appraisal is ordered and if it is in a Special area I.E. the north or south side of a River, Intra-Coastal or oceans then I need to meet the appraiser and point this out.