As I have been doing research it seems like a lot of different vendors are often selling the same diamonds, do not have the diamond in their possession, but can send pictures, and can potentially ''bring it in-house to inspect''.
If they are "in-house" than the vendor actually has them, if not they don''t and many other sources may have them. Sometimes a vendor doesn''t have any and they "drop ship" from another vendor. Do a search for the term "drop ship" to learn more.