Now, you're thinking of course! Farmable items are always going lower and lower but that isn't fully true. See when sell was in place it always made sure the value of an item was above a certain amount and the buy would make sure it's below a certain amount so the the value of non liquid assets always stays within a range. Now since sell has been removed, all items can go as low as 0 but never beyond their buy price. This rases a huge issue! If one and only one player makes a really big farm, say guardian, and is willing to sell his products for really cheap, he can cause the value of that item to drop to whatever he wants. Now that's it is virtually worthless other players will sell for no more than that price and the market for it has crashed. This should logically happen to many items and even if it's not all at once, if the bigger shops slowly lower the price, they can also destroy the value of that item.
See what I mean?Note removing buy is not the solution, then players could also rapidly increase the price and thus the meeble