Yup, now I'm nearly 100% sure it's a fake. The scammer was sloppy. They didn't use the proper model name for a Gigabyte GT 730 on the sticker and didn't make the effort to print out a clock consistent with a GT 730. No Gigabyte GT 730s are clocked at 810 MHz, but what did have 810 MHz clocks? A GT 440. See no other conclusion but that someone repurposed some GT 440 PCBs with a $2 shroud and a cheaply printed sticker + box. I wonder if it was even reprogrammed to read out the correct specs other than changed to GT 730.
It sucks, but on the plus side, a GT 440 isn't really that much worse than a GT 730, just older driver support. There's likely little recourse at this point, unfortunately; no one should ever buy a GPU on Facebook...