An alternative route might be to learn how to grade them for yourself. Get a Red Book and a Photograde and go to it. Then you can compare the "expert opinions" to what you learn. One of the reasons that the rich are, indeed rich, is that they KNOW what's up with their own money. You should follow suit in this case.
But to Bill's point, a dealer is going to give you a "downsized" price, and then try to buy them from you at something like a wholesale price. I aint knocking them - theyre trying to make a living, like anyone else. But its in their best interest to remain calm and work the percentages.
There are also the independent grading services. But, you pay for that and they only grade them, not value your coins for you.
Finally, there any number of coin sellers on the internet and in magazines. Once you know the graded quality of the coin, you can see what they actually sell for at retail. It can be variable and there are no absolutes, but it is best to go with what you know people actually are paying for the same or similar items.
In the end you get a range of value that can be attributed to each and every coin - a market value price if you will. That, in all honesty, is the best you can hope for. We're not talking manufactured goods here like, say, a car, which has definable production costs and a calculatable profit margin. It is only false hope to hear some high number tossed on the table by an "expert," and then expect that THAT is the final value, just because you like the sound of it.
All of this is eclipsed, to some degree, if you happen to have some exceptionally rare pieces. A 1916-D dime in AU condition, for instance, is going ignite a bidding war in your best interests, a very desirable thing. But again, it will be based only on what a buyer will pay and you would be wise to learn what such things have, and do, trade for ahead of time.
While there is a genuine trade in coins that can be determined, the bottom line is that, just like real estate and Beanie Babies...
"Coins are only worth what somebody will pay for them."
