Hi Katbran,
Welcome to P-G!
Your question is not an easy one to answer, and these are just my thoughts on the subject-------------
Akoya pearls are some of the most challenging to evaluate as to quality vs cost. Akoya are more expensive to start with, being cultured in the small akoya oyster, which cannot produce the multiple 24-30 pearls a freshwater mussel can produce. Thickness of nacre is difficult to evaluate, but is all important, because thin nacre can wear down to the mother of pearl bead underneath fairly quickly.
Some unscrupulous "suppliers" know a strand labeled "akoya" may infer to the consumer a higher quality pearl, i.e., akoya=Japanese pearls=Mikimoto.
Hanadama certificates issued by the Japanese govt describe the akoya pearl strand meeting the highest standards. Hopefully you have read that section here.
Although these strands run in the thousands, one is assured that nacre depth has been evaluated by x-ray, the only truly accurate measure.
Some sellers offer with your pearl purchase an appraisal certificate giving the retail replacement value (for insurance purposes). Or you may just receive an invoice that might say "akoya necklace" or something like that.
Akoya pearls are recognizable as one becomes more familiar by looking at and handling pearls. They have characteristic blemishes, fall into a certain size range, nacre has a certain sheen--all subtle ways to differentiate from freshwater pearls.
Most important to purchase from a trusted supplier, with a generous return policy, especially when buying on the internet. A number of the online sellers who post here, offer Akoyas, including Hanadama. Buy the best you can afford!
Vintage akoya necklaces are widely sold on the internet, with a wide range of prices; it is impossible to evaluate the quality just from photos, or what wear damage might be present. One can pay anywhere from hundreds to thousands.
Top quality freshwater pearls have similar luster to akoya, and sell for less when comparing same size strands.
There is nothing like seeing pearls in person and trying them on-------if you have more specific questions, please do ask!
