As far as I know the Natural Sapphire Company is legit but their prices are very high and the cut on many of their gems not so great.
You do need appropriate certification these days, either GIA or AGS or some other well regarded international laboratories.
Manmade sapphire is identical to natural on almost every test you can do without very expensive lab equipment. They are real sapphire, just grown artificially. A natural sapphire might have typical natural inclusions just as a synthetic might show curved striae under magnification but the SG, under a polarscope and dichroscope you can’t easily sort natural from lab grown.