’reliable’ is as reliable as we choose to make it -
that really makes no sense. It is only as reliable as the data and "we" have no choices in that
Something could be sold out desperation, it could be sold as scrap, it could be pristine with warranty, it could have extras like cables or tubes. The data set is too small, the condition of the item is unknown, the circumstances of the sale are unknown, and most of all the actually selling price is unknown since it may or may not be accurately reported and may or may not include fees and shipping.
The blue book is beyond unreliable, in my mind it is pretty much worthless