Dear HVZ,
It really depends on what you mean by fake or legit. They are not fake in the sense that no one really forges these GGL certificates of authenticity. So, in that sense they are perfectly legit.
However, they are fake in the sense that they provide misleading, fake information. For example, the certificate you have here states it’s a natural, heated ruby. In reality, it’s a worthless composite ruby. I have seen numerous GGL certificates of authenticity where it’s said “natural emerald”, whereas it’s a fracture-filled, dyed quartz (fake emerald) in reality.
Thus, in this sense these GGL certificates are as fake as a three-dollar bill. They are happy to print anything on these certificates as long as it helps to sell their stuff.

Dear Edgar,

These rough diamonds aren’t really worth much. Of course, rough diamonds can be very expensive but not in this case. You see, only the lowest-quality diamonds (so-called industrial grade diamonds) are used for making such necklaces. And industrial grade diamonds are very, very cheap.
They also do look rather ugly. I think it’s a bit strange to use them for making a necklace or any other piece of jewelry.
It doesn’t really matter whether it is 16, 20 or even 30 carats in this case. As I said before, they are extremely cheap. 250 for this necklace is a rip-off.
Rough diamond necklaces cost around $20 – $30. Here is the one I found on Etsy. You can find them even cheaper than this.
https://www.etsy.com/listing/616191957/raw-diamond-necklace-diamond-necklace

Dear Ongesa,

No doubt, these are genuine black diamonds. They have all the typical visual characteristics a black diamond would normally have. Thus, no problem with that.
Let me elaborate on this further. The price is unreasonably high for this pair of earrings. This is a rather simple piece of jewelry. Color treated black diamonds are pretty cheap. It seems that the seller hasn’t mentioned anything about treatment in the description, but rest assured that they are color enhanced.
You can get black diamonds like these (or even better) at a price of $60 – $70 per 2.2 to 2.4 carat diamond (on ebay, for example). Mounting settings would cost you another $100 or so + 2 backs at roughly $ 20 per piece (this is what I found in no time; probably you could find an even better deal by investing some time).
So, let’s do the math: (70 x 2) + 100 + 40 + shipping (let’s say another $20) = $300. Mounting is very easy in this case. It should take an experienced jeweler less than 30 minutes. The cost depends on how expensive or inexpensive the jewelers in your hometown are. I’d say it’s maximum extra $50. So, the total cost would be $350.
They sold this pair of earrings for AUD 1200 on invaluable.com which translates into $ 828 + 30% buyers premium = $1076
This is something to consider, don’t you think so? 🙂 $1076 vs $350 😉

It is very much right what you noted about simulated diamonds. No reasonable person would set a real emerald and simulated diamonds in the same setting. This is definitely not an emerald. That’s for sure. It is a bit difficult to tell from the images whether it is a dyed beryl or a dyed quartz. Looks like beryl to me (quartz is usually lighter in color and the color-concentration zones are more pronounced).
As far as GGL “certificates” are concerned, if you see a gemstone with a GGL certificate, it is a red flag by itself. Every single “gemstone” I have seen with a GGL certificate so far has been a fake. So, it is no real certificate.
So, I would say that a Thai or Indian-made silver ring with a dyed beryl and simulated diamonds would cost around $15 – $30 on eBay (ok, maybe $40 if it’s supernice).