What price guide are people using. I have been using NGC US price guide. Prices seem a little different than the Red Book. http://www.ngccoin.com/poplookup/NGCCoinPriceGuide.aspx
I go by how much I'm willing to spend on it. Most printed price guides are already wrong by the time they hit the shelves. Researching completed auctions will give you a better idea of the price trends on particular coin values.
how accurate are numismedia and NGC's price guides? Or are they essentially the same thing? They have my 1958-D Washington quarter listed as $225 for an MS-67, would this be a good price for that?
I use completed auctions, both ebay and major auctions houses, as a guide. I also have a price guide specific to the area of coins I collect, but even that price guide is really just a collection of auction prices with imputed pricing data for grades other than what sold at auction.