Certified quality pearl jewelry is easily available online as well as from jewelry shops and dealers that specialize in pearl jewelry.
Such certification can be undertaken by USGL, Underwriter Services Gemological laboratory. USGL specializes in providing jewelry evaluations for high volume sellers of most types of jewelry. Mostly they evaluation diamonds and gem stones but will also do evaluations on pearls and anytime you purchase a pearl then it should be accompanied by an evaluation report from the USGL or a similar accredited gemological laboratory.
Most of the gemological laboratories are listed on Price of Diamonds.
Unless the pearl you are buying is certified you have no way of knowing if the quality is as stated by the jeweler and, if, you are looking for a natural or an akoya pearl, this should be stated on a certificate of evaluation and not by a statement from the jeweler. Even a written statement by a jeweler is insufficient to guarantee that the pearl is as stated. A gemological evaluation is very important, not just for your own peace of mind but for insurance purposes as well.
It is a good idea to ensure that the dealer is genuine, especially if you are dealing with one online. Does the dealer have a fixed address and contactable phone number? Does the dealer provide a returns policy where you can reclaim your money if the pearl(s) are not up to your expectations?
Mostly it is a case of knowing what you are looking for, ensuring you have some understanding of pearls, and this is easily obtained from this website, and practicing some common sense and due diligence.
This way you can assure that the certified quality pearl jewelry you buy is going to be what you want and will give you a lifetime of pleasure.