GIA certificate is only a proof to ensure the quality of diamonds, which is highly recognized all over the world, that is, an approval of your diamond quality.
Yes, you must buy a GIA certificate when you buy diamonds. GIA is a non-profit organization, and it is the founder who pushed the diamond appraisal certificate to internationalization.
GIA does not price diamonds, nor does it participate in the pricing or valuation of diamonds. GIA's operation does not involve any commercial interests, which can ensure the objective and fair evaluation results of its diamond quality. GIA diamond certificate provides all the important information to help you understand the 4C standard of diamonds, various treatment methods and so on.