SE can just 95% or 90% percentile the prices, makes it work like an actual (regulated) market. In a stock market there is a comission for listing and a comission for buying, and you can only sell at the best price and can only buy at the best price. You simply can't mis-price anything (and this is almost entirely regulated by price arbitration rather than computerized limits, but you can't arbitrate prices when the supply is unlimited while inventory is not) EG 100 sellers selling "Elm Log", the top 5cheapest and top 5 most expensive are dropped from the list and the average price is calculated. The game would then simply prohibit placing prices that are more than 10% below the calculated average or 10% higher than the calculated average. (Prohibiting dumping and illicit gil transfers) However this would only work correctly if you could buy individual quantities, not the entire stack. The entire stack is basically an "all or nothing" equivalent. Or more accurately described as "I don't want to get hit with multiple commissions."
I suppose one other way to solve this is just to deny the RMT and illict gold transfers by not allowing to be bought, or not listing anything more than 100% more than the average selling price if SE were to track the average selling price. Likewise denying one-way/uneven trades of that design as well.