This area is famous for BUYING jewelry

http://www.diamonddistrict.org/home.html

But has anyone ever SOLD their used jewelery in the diamond district? Sold diamonds, scrap gold, old rings that you don't want for their gold or silver value, estate gems, etc.

Just wondering. How'd it go?

Not in the Diamond district - but I discovered that if you take your old gold to a jeweler who deals directly with the refiner, you get a better price. Just about every pawn shop is buying gold, but it really does pay to go to the pros.

Klim Jewelry on 66 West 47th street in NYC is ok, but to max out gold value to cash you can buy up to something you want like diamond jewelry or a nicer gold chain. West 47th street in New York City is the main place to go, but there are shops around that area so walk around. They mostly have long reputations to protect so they will not screw you if you know what you are doing.
Shop around for best price. Don't let them suck more than 10% off actual gold content value. Items not clearly marked in carat are the items they will argue about. If its marked you should get near its value. Deal in cash. use grams, penny weight and troy ounces. 24 carat is 100% gold. 1 troy ounce is 31.1 grams. 20 Dwt (penny weight) is one troy ounce.
Philadelphia has its diamond row near the Independence hall, they have fewer stores but will also buy gold for cash. expect to be finger printed in some cases. The more reputable stores what to assure its not stolen.
Have to go weekdays from 9-5 to get best stores open FYI, in both places.