Im not sure..but if its worth lots of money i would prefer to buy from the store...especially gemstones, you have to have it checked by a gemologist or something to know if its real...i dont know how long it takes to have it checked though...it may or may not exceed the return period..
I have purchased 4 or 5 rings from ebay seller Vintage estates . I have had nothing but top quality and excellent service. They don't have items all the time so you have to save them as favorite sellers and check periodically. They are extremely honest and have 100% excellent feedback. Personally I won't buy anywhere else. I purchased alexandrite rings, a blue sapphire and a ruby ring. I have seen emeralds on their site before. You may want to check them out and you could always email the seller with exactly what you are looking for