In other words, don't trust them! Don't sell it to the first jeweler, as girly says. Get a quote from a few, come back home, sleep on this, and then ask a double price from the one that gives the most, and see what he says. I am serious.
If this ring is for real, they will offer you all kinds of seemingly great deals, just to make you surrender it without thinking. Like only today they have a great client who will give you twice the regular price, etc. Don't buy into it, it's a standard trick. Make sure you have several quotes, and then bargain as hard as you can. 