I think the reason of as you say, guru not having alot of sales that go for buyout, is simply because alot of people use it as a "long time" sale medium.
The stance people take by trading here is making sell threads for their items to soak up exposure, which will demand time and thus makes the waiting a factor of certain r/bs being closer to its b/o.
If you would sell it for any urguent reason, the b/o reflects most of the times that there is room for profitt. (if such intention is there.)
Kamadan has become a playground for people these days, to fool others with proclaimed price checks in the hope they could benefit from if the oppertunity allows them.
And the victems are either people that last logged in years ago having perhaps q7 weaponry, or new people deciding to play gw(1) since they enjoyed/disliked gw2.
As last I think people in big alliances just ask their own ally for PC's and thus taking the majority that reads it as truthful, its a risk factor but also.can lead to further under/overpricing.