I would venture a guess that it has to do with the vendor and the venue. Is it offline, online? I notice that sometimes on Pscope searches, some unbranded H&A's from vendors we don't really hear too much about (like an 'IceStore' or similar) are more $$$ than something like an ACA or a SC. What does that mean??? A sucker is born every day.
The presence of an H&A pattern within a diamond does not necessarily command a premium over an ideal cut diamond which does not exhibit a crisp and complete Hearts & Arrows pattern... The way a diamond is purchased has more of an effect on the price it is sold for provided that all other factors such as carat weight, color, clarity and proportions are equal... A diamond brought in on memo (consignment) by a dealer will cost the dealer more than a diamond purchased outright by the dealer and thus it is likely to sell for more too... We stopped allowing our suppliers to charge us a premium for diamonds which exhibit H&A patterns years ago because we buy our inventory as opposed to bringing it on memo and thus our annual volume provides us with a certain level of negotiating power... No doubt other dealers who buy their inventory also benefit from similar advantages...
On a side note, your thread might have been noticed faster on RockyTalky than it was here...