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Filter outliers from Steam Community Market prices


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Pretty simple thing that isn't a huge deal, but mind as well suggest it anyways, implement a check to filter outliers when calculating the average SCM sale price for items that aren't priced via suggestions.


I.E. if you have a specialized killstreak eviction notice fabricator that has 12 sales at $0.03 USD, the site will omit/ignore a sudden $300.00 USD sale because it is very clearly not a valid sale. Or in the case of items of actual value, say a specialized killstreak australium has 30 sales in the past month at right about $25.00, then suddenly a $60.00 sale, said 60 dollar sale gets ignored because said item was probably either spelled or signed by someone significant and wouldn't be a valid sale in an actual price suggestion as a result.


Alternatively, but much more rarely, you can have an item that's worth a lot of money be sold for $0.03 USD to artificially lower that item's value and try to get items for cheap through that, though it wouldn't be worth the money and I have zero clue how you could set it up to be guaranteed to just buy it yourself on an alt account, not to mention how most people aren't dumb enough to fall for it.


There are three problems with the algorithm factoring in outliers:


1) Fake voting power

By far the least significant problem, users can find fabricators / other cheap items with an outlier causing their price to spike to buy a lot of said item and artificially raise their backpack value enough to vote on / make suggestions for items they shouldn't have access to doing so with. This basically doesn't matter though since voting doesn't matter and you can already make suggestions on anything you want without needing the proper voting power.


2) Item owners mistaking the value of their items

This isn't really a big deal, but there's a lot of newbies that will come to the site and see they have a junk fabricator with a $50 USD price tag on it because of one outlier sale and will try to sell it for that much. Causes no real harm, but does give them the wrong idea.


3) This CAN be used for scamming (kinda)

This is the actual big deal, although it'd be hard to pull off as you would need to find a player who is new to the game, doesn't know item values, and doesn't know how to check the steam market. If you obtain a fabricator that has an elevated price due to an outlier sale, you can get a few and try to find newbie players to scam for them, as you would be able to link them to the item on backpack.tf to show that it supposedly sells for far more than it's actually worth. Alternatively you can maaaybe artifically lower the price of items via what I said in my 3rd paragraph up above, but that's more than likely extremely impractical. I doubt that any of this is a practical scam method or that it's ever even actually worked on more than a few people, but it's still something that might be possible which the site would be at least partially responsible for due to giving misleading information.


I'm unsure of if it would actually be easy to implement this change or if it's deem worthwhile, but just for point #3 I feel that it'd be better safe than sorry to look into this when possible, even if it's probably the weakest/least-possible scam method I can think of.

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11 minutes ago, FP jh34ghu43gu said:

How do you find outliers on low volume items ie collector handshake. It sells like <=2 a quarter which is plenty of time in recent years for a dramatic price hike to occur.


It'd ideally be based on sample size and thus items with too low a sample size can't have this applied to them. I.E. An item that sells one copy every week at best would be ignored, while high-volume shit like fabricators would have the check in place.

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There's actually a very easy solution for this - instead of using average price, use median price. So if we have 5 sales of a fabricator:







The average price would be: $1.04, while the median price would be: $0.04.


I think SCM is using median prices for high volume sales items to create the graph, which seems like the most fair price.

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