I remember a couple of months back when I was at a stamp & coin store a man walked in and just had to sell his mothers coin collection. Out of interest I just hung around as the man brought in several of those large plastic tubs in filled with mint year sets.
The price offered was not much over face value or the set price of silver. I'm not an expert on money but it was sad to see him offered only face value for several of the old bills. In fact the dealer told him he might be better off spending it.
Certainly any grilled Washington that is Mint can bring in some good dollars depending on how it is graded. Off the top of my head there are at least 7 different Washingtons with grills. The prices will really swing with the grading.
For example take the #96 F Grill Yellow black Washington. If it is used and in average condition it will bring around in anywhere between $35 and $59. If the condition is better it can bring in anything from $100 to the $900's. if it is mint an average stamp might bring in about $500 and the better grades $1,500 plus.
So you can see grading on the classics are important and more important you should know something about grading the stamps. This is not something I would let up to the person or dealer who will be buying the stamps. It is best to take a while to learn about your stamps in order to get the top value if you do in fact have a lot of the classics between the years 1847 and 1900.
Most important though is that you understand the market place for stamps. You might want to look through this web site just to see the difference in values that I have reviewed. It is a good reference though just part of the full picture picture when trying to figure out the price of stamps.
http://www.stampwants.com/index.php