I hope GAtor wont mind if I make a comment or two with which he may or may not agree in all respects - but if not he'll doubtless say so.
Demand sets value, not value demand. (Look at Mystery Tales.)
And then there's Hollywood.(Thanos anyone?)
No price guide can stay on top of market responsiveness such as that, and therefore Bob Overstreet tends to be consciously conservative about hiking value because he takes a very long view about trends (or at least he did last time I bothered to check about ten years ago when I last bought a guide!). So if value on a given book or genre climbs consistently and maintains that level he'll eventually get round to acknowledging it. But GAtor is absolutely right to say that the true value of the guide is far more in it's function as a reference.
It also becomes absurd when collectors cite GPA as if it is a price guide.
I just sold my FF #12 9.0 white pages in the C'link auction. Check GPA and you'll find huge variation on prices for that book in that grade - quite impossible to use the information to predict an isolated sale.
So for a sense of what something is worth, I look less to GPA or Overstreet, and more to dealers I know, because they have their fingers on the pulse.
A dealer - which I'm not by the way - I lack the discipline or the skills - is running a business and is obliged to charge what s/he thinks the market will bear. Dealers whose businesses flourish tend to be very astute at gauging the market, which stands to reason and should be obvious.
Dealers also want to build up long term repeat custom based on bespoke relationships wherever possible, and this too stands to reason and should be obvious.
The onus is on the buyer to determine whether they are comfortable with the price.
And I go back to those dealers who give me reason to.
Take a bow, GAtor, and Mr Bedrock.