My approach is straight forward when dealing with coin or jewelry dealers. I ask if there is any info that they can give me about the said object and explain that I am not interested in parting with it. If the store is not busy 90% of the time they will pull out a loupe, diamond tester or even test the object just to authenticate it and arrive at a retail price in their head.
You just have to let them do most of the talking. They want to find out specifics because the dealer may offer you $$$ even if you come in with the base of "getting info." This holds true for private shops. Retail chain jewelry stores will have ya send it out and pay probably. I never explain that I found it (just for safety), I always blame my wife for having spare jewelry that she doesn't want and use that for my argument or say it's a sentimental piece that I always wanted to know more about.
The guy who offered you $40 is as useless as cash for gold.com. Shop around. Take that ring to several places and watch how much the dollar value opinions vary. Stay FAR away from pawn shops. Ok, go to one and see how horrible their offers are. I realize that they need to make a profit, but largely they are kept in business by thiefs, addicts and very desperate folks who need cash fast.
Just my take on what I've experienced. The best way is to learn a little about jewelry is through books and on the internet. The true beauty is having access to a dealer who will give a "fair" price. You need to know what you have before you take it to sale so you can get the maximum $$$.
