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Both tasks are common in the real estate world but each one is used for a different purpose. Estimates are more general calculations made when more exact calculations are not necessary. Estimates are often prepared for the purpose of putting a home on the sales market. Estimates can be made by anyone and are often made by real estate agents themselves. On the other hand, appraisals are more exact calculations of value and take into account a number of scientific factors. Appraisals are often required for tax and loan purposes (e.g., to figure out the tax liability of a home owner or to figure out what type of mortgage someone will need). Appraisals cannot be conducted by anyone and must be completed by trained individuals. Always make sure a property appraiser is licensed or certified by the state to perform real estate appraisals. While state licensing and/or certification isn't always an indication of quality, it ensures that an individual has met certain standards and is authorized to perform property appraisals. Some states do not require licensing to perform real estate appraisals.  At the state level, there are two types of property appraisal licenses: the State-Certified Residential Real Estate Appraiser would be the minimum license to consider. If it's a typical residential property you want appraised, you will want a State-Certified Residential Real Estate Appraiser, as a minimum qualification. Don't be afraid to ask an appraiser for a copy of his or her license. Once you get a copy of the license, it's a good idea to check with the government agency which issued the document to ensure the license is active and in good standing. Furthermore, you can view the U.S. National Registry at http://www.asc.gov and verify whether the appraiser is registered and eligible to perform appraisals. Many excellent real estate appraisers carry a professional designation. The most widely known industry designations are the Senior Real Property Appraiser (SRPA), Senior Residential Appraiser (SRA) and the Member Appraisal Institute (MAI). These designations are issued by the Appraisal Institute, and demonstrate an appraiser's commitment to continuing education and ethical standards. Ask what their experience is working on the property and neighborhood you are looking to get appraised. Appraisers who do a lot of their work or live in a particular area often have a deep knowledge of property values in that area. Additionally, they are more likely to know how "neighborhood variables" such as school districts and fire departments affect the property values in the area. Although years of experience does not necessarily indicate quality, there are certain benchmarks quality appraisers will have met. It usually takes about five years to get a good working knowledge and competency. If you find an appraiser in the yellow pages, you might not have much information about them. It can be useful to crowd source people in the industry. Ask a lender, real estate agent, attorney, or accountant for an appraiser they have used in the past. You'll still need to inquire further into their qualifications, but finding someone who has experience with the appraiser is a good start. You can also use the internet to find information about an appraiser's credentials, customer experiences, and history of complaints. For example, in California, the Department of Consumer Affairs, Bureau of Real Estate Appraisers has a search function on their website. Using the search function, you can find information about any licensed appraiser in the state.

Summary:
Determine whether you need an appraisal or estimate. Make sure they are licensed or certified. Ask about their professional designations or memberships. Inquire about their experience. Ask around for references.