The difference between a natural and a synthetic (Man Made or lab created) emerald imitation can be difficult for the average person to determine and far more difficult if the gemstone is set already in a metal mounting.

Never inspect a ring without a X10 lope, if you don’t have one, ask the seller for a 10x lope or a good magnifying lens and a bright light. If you see tiny flaws or "irregular patterns" within the stone and (this is a very important detail) small natural holes or tiny deep lines especially in the pavilion (the backside) of the gemstone, this is an indication that it may be a natural emerald.

Make a very sharp inspection on the girdle of the gem looking for material fused together or assembled in layers If you don't have access to inspect the girdle and pavilion, I wouldn't buy the item, there is a lot of tricks like doublets made with the same material of emeralds with identical characteristics of them and color enhance in the mounting among many others. If you are buying a bezel setting emerald ring make sure it has access to the pavilion for inspection and further cleaning process. But also there are emeralds and other color gemstones with a remarkable color zone... If you are buying ONLINE a ring where beautiful computer renderings are shown, this means you are ordering a customized piece or a special order item that is not returnable for refund or exchange. This is normally why these jewelers specify two weeks to ship your item. Most retailers Online display impressive computer made renderings (not photographs of the actual item you will receive). What they are offering does not exist yet — at least it’s not already finished and ready to ship to you. So gold mounting has to be ordered; the right gemstone (size, color and quality) has to be located and then the gem setter has to make the item. This is a much more expensive way to buy because the store is ordering a single piece in addition to a normal 50% of profit —> all included in the price you have paid.