"Diamonds Are Forever"
That's not just a slogan, but a fact of life. Jewellery companies are happy to SELL you a diamond at "retail" or "appraised" value, but don't ever expect them to buy anywhere near that price, and that's even if you can get them to buy a diamond from you at all. In fact, most jewellery stores have a policy against buying diamonds from customers. There's a good reason for this.
The world's supply of diamonds is controlled by the DeBeers family, and they've spent many hundreds of millions "educating" the public of the "fact" that diamonds are rare, valuable, and "forever." That's because in truth, diamonds are NOT rare, have relatively little inherent value, and it is only the fact that they've made it nearly impossible to RESELL diamonds that they can continue their fiction.
In an open market, most diamonds would sell for less than 20% of their current retail price, with rare exceptions for large, near-flawless diamonds, which ARE rare. But due to the DeBeers monopoly and that family's strict control of the market, just enough diamonds are put on the market each year to meet the demand while keeping prices artificially high. And because retailers can buy diamonds at WHOLESALE prices (about 20-25% of "retail" or "appraised" value), they would lose big money buying a used diamond for anything more than 20% of retail. And, because they know very well that offering a customer 20% of what that customer THINKS their property is worth is going to make that customer very angry, few retailers will buy diamond jewellery at all. When pressed, they will often refer a customer to one of the few shops that will buy the diamond. These shops are used to giving the customers the "bad news".
Anyway, don't be surprised at the lowball offers, assuming he gets any.
-Troy