An accurate appraisal involves the combination of skill, technical expertise and years of experience.

You need to bear in mind that works of art, apart from their obvious aesthetic and historical value, have a monetary value too. Dealt with correctly, you have an object whose economic value can be easily converted into liquid assets, but this depends absolutely on an accurate expert appraisal. 

An accurate appraisal (which may perhaps advise dividing objects up into homogenous lots) can be of great help in avoiding possible conflict between beneficiaries when dealing with inheritances for example.