Value is in the eye of the beholder, but basically it comes down to supply and demand. Timing can be a factor, we all have seen chips up for auction and not get a bid, then they are put up again and the bidding goes crazy. Ask what you want for the chip and if it sells fine, if not it may be that the right buyer just did not happen to we watching. The guides just give you a general idea of what the chip was valued at when the authors were valuing the chips.