As far as I know, if you take them anywhere, a dealer or store will only trade up for you by considering the WHOLESALE price of the diamonds you brought in. So, basically you will be losing a LOT of money. You can't really take diamonds to somewhere else other than where you bought them and expect to get anything more than wholesale for them, even if you are trading up. Consider that if you take them to a store and pay extra to trade up for them, that jeweler still has to sell them.....so they look at it as why should they pay you retail for a pair of earrings when they could purchase them from a dealer/broker for wholesale?
If I am wrong, please let me know PFers, because I would LOVE to find somewhere that does not give you wholesale or less for your diamonds when trading up.