Article in English: Buy valuable gems from a trusted source. Be sure that the jeweler has an established reputation.  It is best to find a jeweler with a return policy for products that are sold with inaccurate descriptions of clarity and quality. It is a good idea to have very expensive gems (or gems that are three carats or larger) appraised by a third party. It is best to use an appraiser who holds membership in the American Society of Appraisers, one of the oldest appraisal societies in the United States.  To find an appraiser, take the following steps:  Search the American Society of Appraisers’ website here. Click on “find an appraiser,” then enter your zip code. Type in “gems and jewelry” in the appraisal expertise section. Select an appraiser from among the search results. In order to appropriately evaluate the value of an emerald that you are considering purchasing, you can request an AGL report, which identifies the type, size, cut, clarity, color, and origin of the emerald you are purchasing. This report will give you some degree of confidence as to the quality and value of your gem, even before getting a third-party appraisal. Before purchasing an emerald, you should be sure that you are getting a good quality gem for the amount of money you are spending.  An AGL report will give you a starting point, but the AGL may not represent accurate market value (AGL report prices are often inflated).  To get a better feel for fair pricing, you may want to shop at different jewelers, taking notes about the color, cut, and quality of each gem that you are pricing. Keep in mind that pricing a stone is ultimately subjective, so you cannot necessarily come up with a specific “formula” for the exact value of a stone. Emeralds are often treated with oil or resin to improve the stones clarity. This is done because of the emeralds Type 3 nature which means its naturally included. Clarity enhancement is common practice and is considered an acceptable enhancement to the appearance of the gemstone unless it is treated with dyed oil....

Summary in Vietnamese:
Chọn những cửa hàng kim hoàn có danh tiếng. Định giá viên đá. Yêu cầu chứng thư giám định đá quý từ trung tâm giám định đá quý có danh tiếng như Trung tâm Nghiên cứu – Kiểm định Đá quý và Vàng (VGC). Hiểu về giá. Hiểu quy trình xử lý tráng dầu.