The idea that the Audiogon Bluebook is "reliable" is hilarious
any source of data needs to be understood for what it is - reliability is in the eye of the beholder, so to speak
a-gon bluebook tracks sales through the site over time... thus it is primarily a usa based data set, and it produces calculated ’averages’ over time for any given component
on most components with ample sales data, one can see a graph of prices at which they changed hands, as a function of time... so for an older, popular component (let’s say a c-j pv14 linestage) it will track from when it was pretty new, to the present, where it is now decades old - so the nominal ’average’ does not take into account the first falling, then later, stabilizing prices (a common depreciation curve) - one can also see the spread between ’mint’ units with ones in less wonderful condition, which can be useful
so like all other data sources that one can consult to inform buying or selling decisions, one simply needs to understand what the data set is, how it is gathered, how its presented ’answers’ are computed, and how one may need to ’peel the onion’ one layer or two to gain more insight
’reliable’ is as reliable as we choose to make it - like many things in life, getting good answers, making good decisions, being really informed, takes some effort and determination