Inconsistent priority given to some buy orders on Steam Market

I have been using Steam Market for some years. Several times in the past, I have been surprised by:

the priority seemingly given to some buy orders which were lower than the bid,
even though the item in question was a commodity.

For reference, this is how "commodity" items are described on the page of a market listing:

This item is a commodity, where all the individual items are effectively identical. Individual listings aren't accessible; you can instead issue orders to buy at a specific price, with the cheapest listing getting automatically matched to the highest buy order.

Earlier today, I was able to get a screenshot of this seemingly inconsistent behavior for sacks of gems, which are commodity items. In the screenshot below:

the ask is at 0.31 €,
the bid is at 0.30 €,
there are more than 5 thousand buy orders at 0.29 €,
the user jmakela4228 buys an item for 0.28 €,

For reference, jmakela4228 happens to be one bot of one of the largest networks of bots (if not the largest network) operating on Steam Market. If you often buy or sell trading cards and booster packs for the less popular games, you are bound to encounter one of these bots.

If you check clees42's profile, there are 640 similarly named bots in his list of Steam contacts, and the main account has 158 thousand market transactions by itself.

I wonder whether it is:

an exploit,
a display bug, and the buy order was not actually fulfilled for the displayed price,
the result of rounding in a currency stronger than the euro (EUR €), maybe the pound sterling (GBP £).

The fact that the buyer is a bot could be a coincidence, as it is expected that one of the biggest botnet in the gem/card arbitrage business should also be expected to purchase large volumes of gems at regular intervals.

Potentially relevant threads:

1 Answer

I have asked this question on Discord to one of the most prominent members of Steam Community Market: the creator of ASF and an administrator of Archi's SC Farm (more than 1.5 million members).

He confirmed that the description is misleading: the implementation of buy orders is not what one would expect.

Basically:

with 30 unrestricted bots, you could set 100 buy orders at 0.01€, 0.02€, ..., 0.30€ with each bot, for a total of 4.65 €,
then perform transactions at prices lower than the bid, skipping the queues of people with higher buy orders, whenever a seller nonchalantly sets a sell order below the bid, maybe expecting the Steam Market to work as in the description.

For reference, if you try to buy an item, the dialog box contains the mention of a maximum price: you are guaranteed to spend at most the amount mentioned in your buy order.

This is the most you can end up spending as a result of this buy order. Items will be purchased at the cheapest price available, so the order may end up costing less than this amount.

In contrast, if you try to sell an item, there is no option of a minimum price. To the contrary, it is written that the buyer will pay the exact amount mentioned in your sell order.

I believe the system is set-up this way to passively enforce the ceiling on Steam Wallet balance.

Currently we are restricting Steam Wallet balances to $2000. In other currencies, the limit will be set to a value close to $2000. We also limit the maximum price of a single listing on the market to $1800 (or similar for other currencies). You will be restricted from listing items for sale in the Community Market if the existing balance in your Steam Wallet, plus the sale price of the item(s), would together exceed the $2000 limit.

Even if this asymmetry between buy and sell orders is intended by Valve, I am surprised that pre-existing buy orders are seemingly given an inconsistent priority when matched with a sell order.

Indeed, as I mentioned in a comment below the question, I have placed hundreds of buy orders in the past, and I have always paid the exact amount mentioned in my buy borders set at (or below) the bid, never less. So my experience is consistent with Archi's statements: a sell order which is below the bid seems to be matched with a buy order: