Unless someone else comes on here with different information, I would have to agree with David & Toni: It's a seriously stoooopid markup racket. Not at all like melt-value of gold, which removes all doubt of retail verses wholesale (melt) value. Toni's statement of "anything less than a karot" having "little value", I'm afraid to say, is probably true. You can see 1/3 and 1/2 karot diamonds going on ebay for a pittance

Certainly some dingbat is paying $2k for that 1/2 karot diamond in a jewelry store, but the actual intrinsic value of it is worse than the "new" car and "10 minute old" used-car rule.
And David is right about the "appraisal" values being very much an insurance thing: If you get something appraised for $5k, for instance, that simply means what you would expect to have to pay, like if you had to buy another like-piece, new, at a jewelry store somewhere. It does not mean that's what you could expect to
SELL it for. Doh! Jewelry, as far as diamonds, is very much a fondness by a particular buyer, for a particular stone: Whereas gold is bought and sold daily, melted & re-used to infinatum, diamonds on the other hand, are like your pet dog, where you might have paid a lot of money for that puppy, but are going to have a hard time selling him for the same amount later when he's grown. I know that's a poor illistration, but still though, you have to find the actual person who's actually buying stones, to set into new pieces, and know what his sources are selling stones to him for. And as you know, the markup price for stones is going to be astronomical. Because a jewelry store, might only sell a ring or two per day or per week, so they have to make all their markup on just those couple of items, to keep their store open! Ie.: the rent, the utilities, the sale-staff payroll, the glitzy glass counters, blah blah blah
And the cost for appraisals from gemologists (if you are really serious about selling, you're going to need this cert.), is not cheap. So don't even bother with 1/3 to 1/2 karot kinda stuff, unless you're fairly certain you've got some super high grade type of cut? And the range of error he's allowed between grade opinions, by the grading associations, is something rediculous like 2 grade points of plus or minus error range? Thus you can often get different grades from different gemologists??
So for these reasons, I will probably treat anything less than 1 karot, as a "chip".