1. Watch if the seller has certification from international labs like IGI, GIA, etc. for the gemstone or jewelry or has many stones listed with these certificates. In this case, it's a high probability that even a non-certified stone is genuine natural.
2. Never believe on those local certificates that do not have treatment mentioned, especially in the case of sapphire, ruby, and emerald gems. As then even if the seller mentions the stone as untreated or unheated because those are surely treated stones
3. If possible, you can ask for a clear video of the stone before payment.
4. Reviews on eBay are not fully reliable, as even those sellers who sell fake in the name of natural have positive reviews. So use your discretion.
5. Watch all photos and videos of stones clearly and compare prices with other sellers.
6. You can ask us for free for any suggestions and advice on quality to price.