It's because so many people have bought it for 13ish mil that that's what becomes the new standard price for it. If people stop buying over priced items, then the market stays steady.
If there's a supply, and no-demand for it, then prices will eventually fall until people start buying that supply. Then economy reaches near equilibrium, and that's when prices start fluctuating again. Example for this would be the +7 Guard[Tirfing] for 13 mil. Let's say we have 15 people trying to sell these for 13-14 mil each. Not many people would want to buy this item for that price. Thus none get sold. Eventually the vendors realize that their item is not going to get sold for that price, and that's when they start lowering the prices. Say now we have 10 vendors selling for 13-14 mil, and now 5 vendors are selling for say 11-12. People will begin to see that the prices are dropping, but yet the price is still not at the range that most people would buy it for. Let's have 2 people buy the 11-12 mil +7 Guard[Tirfing]. We now have 10 for 13-14 mil, and 3 for 11-12. The demand for all these items has all but disappeared due to an unappealing price. More people start dropping their prices, 5 more drop from 13-14, to 11-12, and two 11-12 drop to 10 mil. Now the people wanting to buy these items see 10 mil (a fair price in their eyes) and those two are sold quickly. Now people might have seen these two 10 mil Guards on PC Bot (just a theory) and when they tried getting them, they were already gone. Now they advertise they are buying this item for 10 mil. Eventually word spreads and more of these items prices are dropped to be able to sell. This goes on and on until eventually Our supply = the demand. This is what we call equilibrium. Eventually, though, we break our equilibrium because the supply has dropped, and there is still a demand for these items. This is when prices will start to rise because the people who want the item, now can't get it. They start advertising that they want to buy it for 11 mil..... no one is selling. Someone else says they want it for 12..... no sale. Eventually, a desperate sap advertises that they are buying it for 13 mil, they get the sale. Other people who may need money start selling said item for 13 mil again.... desperate people start buying for that price.....And our cycle continues. It's Economics.... and sadly it won't change anytime soon.
