Rosy,
At the right price, probably. The key is in the money and the desirability of the trade-in stone. Many dealers are fairly specific about what sorts of stones they sell and they will not be interested in owning a stone that doesn’t do well in their store. They obviously also won’t be interested in paying more for a stone than they would otherwise have to from their regular suppliers. Many dealers work on pretty tight margins and there isn’t a lot of room to play games. They are unlikely to offer what you paid at retail and it may be considerably less. Many dealers are hesitant to get into this conversation precisely because it tends to upset customers when they criticize the stone, the grading or the price and this isn’t usually a good way to make a sales presentation.
It’s pretty easy too analyze a trade-in. Figure out how much you could otherwise get for your existing stone and what you otherwise should expect to pay for the new stone or one comparable to it. Subtract. If this number is bigger than the amount you will need to bring to the table for your trade in than you’ve got a good deal. Otherwise you might want to reconsider unless there is something else about the deal that’s attracting you.