We went to a shop that buys gold, jewelry, etc. with a good reputation in a major city to sell our stuff.
If they throw it on the scale and give you a percentage of "spot," they are likely being fair. That percentage should be about 70-80%. And they should distinguish 10k from 14k from 18k. If the jewelry piece is not marked, they should test it to determine the percentage of gold.
Loose stones aren't usually worth much, if anything. They want the precious metal, not the stones. Be glad if they take them off your hands.
When you go, the buyer should look at each and every piece individually through a jeweler's loop. If he just weighs the lot without looking or testing, you're probably getting ripped off.
And ask him to give you an offer. If something doesn't smell right, don't take the offer. You can always go to more than one store. You can always pick up your goods and walk away.
The first jerk we went to underbid terribly and tried to sell us on getting paid in "crisp, new hundred dollar bills." If they think you're poor, they'll assume you're happy to take anything.