There are always exceptions to the rule. Here like everywhere else.
Recently a well respected club member sold an A/C chip for a mere fraction of it's value right here on the board. I'm sure it was as a result of not knowing the real value but there was an example where one sale would not represent a true value.
One must remember a chip guide is exactly that a guide.

Values change as a result of not only finds but collecting interests, the economy etc.
A good example here is the prices fetched by many Hard Rock issues compared from a few years ago. The issued amounts didn't change but collecting interests did.

For those that weren't around during the Hard Rock feeding frenzy, HR had a good marketing program in many cases creating an artificial value for their chips.
The same people that complained about waiting in line for hours or complained about not being able to get any or enough now complain about the low prices they fetch