When choosing an appraiser, consider the same factors you would when deciding on any other professional service. Check their references and get a recommendation from a trusted source. You can usually find an appraiser at a commercial antique dealers or a major auction house. For unusual items, you may have to go to a sociality dealer. A museum or gallery may provide a list of reputable appraisers they have used.
Some institutions do allow staff to make appraisals on items of low value.
Insurance companies and banks may also refer appraisers they have used. Look for an appraiser who is familiar with your type of object. When choosing an appraiser, it is a good idea to find an arms-length source. Keep in mind that appraisers are not regulated. Some professional associations do have requirements for membership.