The short answer is, diamonds are controlled by a cartel with literal warehouses of diamonds kept off the market to maintain artificial scarcity, compounded by very successful marketing to increase the perceived value above actual value, raising demand. If you are buying new diamonds, you are always paying too much, although how much extra varies.
I didn't know it.
For my enlightenment, can you tell me how a diamonds monetary worth is properly established so I can check if I'm to pay overprice?
They're all overpriced, diamonds are a scam that's so normalized most people don't realize its a scam.
You as a normal person can't really sell a diamond for anywhere near the price it cost you. Even though almost nothing can damage them.
Gold has a spot price and you can generally sell gold to a jeweller for spot minus a small margin. Not so for diamonds.
Just avoid buying diamond jewelry. They dramatically lose value as soon as you walk out of the jewelry store.
Here's an informative video on the subject: https://youtube.com/watch?v=PYUMKRwJzNg&feature=share9
The short answer is, diamonds are controlled by a cartel with literal warehouses of diamonds kept off the market to maintain artificial scarcity, compounded by very successful marketing to increase the perceived value above actual value, raising demand. If you are buying new diamonds, you are always paying too much, although how much extra varies.