Bill F will chime in when he sees this. He follows the current market pretty closely.
Strangely enough, demand across the board has been a bit lackluster lately. There have been a number of early OPC auctions in the past few months, and stickers & puzzle pieces that would have sold in the $20 to $30 each range in prior years, sold in the $3 to $10 range in lots w/limited interest. Very high grade stuff does cause the pricing to spike on certain items (as Dave has recently pointed out with the crazy 4 figure psa9 diecuts & we saw w/ the unfolded toadal poster selling for $700+), but other than that, believe it or not, Greg's price guide has been pretty accurate overall over many years. There are exceptions for some very htf items i.e. diecut number variations will typically pull good prices - better than he has listed, especially in nice condition. I wonder if it's a self fulfilling prophesy? Many people use that price guideline, and the prices have held pretty closely to it.
If you have any specific items in question, I, and I'm sure others too, would offer an opinion.