Just a quick idea from me. The problem here is that players that dont know the values are sometimes willing to buy overprices cards bcs they just dont know better.
Implement an easy average estimation of a cards price on top of each card in the AH.
For example if a card is sold in general for 100 BFP and someone buys all cards of the same kind...lets say 20 cards...the person has to spend 2000 BFP.
So in the background this would mean, that the general price or you can also call it recommended price for a card shows up as 100 BFP.
If this person now puts in these 20 cards all for 200 BFP each the shown recommended price would not change until the person sells one of these.
If the person sells one card for 200 bfp...the formular would be something like (20C*100BFP+1C*200BFP)/21 ~ 105 BFP
So by selling 1 card for 200 BFP after buying 20 for 100 BFP the average(recommended) price would only rise by 5 BFP.
That means that even new players would be aware of the average price, by looking at the shown recommended price for each card, EVEN IF someone buys all cards of one kind and places them at a absurd high price in the AH. So even if the person puts in the 20 cards for 200 BFP the recommended price would still be showing 100 BFP.
It would even show up when you are about to put a card in the AH. You choose a card to sell and the game recommends you a price to sell it for.