1) Where are you geographically located? For example, do you want someone located on the West Coast when you are located in Florida or North Carolina?
2) Are they a licensed diminished value appraiser in your state?
3) Will they walk with you until settlement is achieved and provide case-specific help? Will they go to court if necessary and if so how much does it cost?
4) How are the Google references and reviews looking on the appraiser you are considering?
There are many appraisers out there. Make sure the one you choose will be able to fit your needs and have the qualifications to back up your claim.