@[DE]Rebecca and all.
One thing that needs to be asserted is that rivens are not meant to be an investment instrument. Anyone who treats rivens as an investment instrument can sooner or later get motivated to manipulate prices whether in an organized way or through their own creative methods. The focus for DE should be to ensure that people buy rivens for their own personal use and not as a method to boost their platinum income like with most investment instruments in real life.
The second concern is about deliberately manipulating riven trade prices. It's hard to judge if certain trades were "deliberately" placed to skew statistics. But it is possible to discourage players from doing so reasonably. Allow me digress from the topic to cite an example from real life. Everyone wants the best security systems in their home to keep their assets safe while they are away. But the more sophisticated the system is the higher is its operational cost. So there's a trade off between the value of assets one wants to protect and the amount of investment that would be considered reasonable to protect that asset. The most "practical" solution is to have a security system that requires more effort and resources for a malicious user to break than the actual value of assets it is protecting. The underlying principle is to discourage malicious intent. Now how is this scenario relevant in case of rivens?
We don't need the most sophisticated analytical tools to police the riven trades if we could only make it less worthwhile for those who are seeking it as an investment instrument.
Have a cool-down period for individual rivens in trades before they can be traded again. I know at least one popular gaming platform has implemented this for items that are traded between players and have the potential for their prices to be manipulated. The cool-down period could be either (1) fixed duration like 2 weeks or may be a month or (2) a function of the value it is traded for. For example, a riven traded for 20 plats would have cool-down period of 24 hours whereas a riven traded for 1000 plats would have a cool-down period of 2 weeks or more before it can be traded again. Of course, for rivens traded with other mods/items/rivens there should be a fixed cool-down period of, say, 2 weeks for all the rivens involved in that particular trade irrespective of their platinum value. Of course, the duration used here are not suggestive but only for illustration only.
[Note: The cool-down period may be flexed like the platinum cost of rushing a build in the foundry, but lets not get there, not for now at least.]
Trying to manipulate riven trades by frequently re-trading the same riven (before its cool-down expires) would then require the riven to be traded at lower values thereby negating the motivation itself.
It may not be the most assured method but I believe this method has (1) reasonable checks and balances to discourage the riven prices from being manipulated statistically (2) can be implemented within reasonable development effort and resources. (3) has no impact/inconvenience for average users who trade rivens for their own personal use or as gifts.
P.S. I am relatively new and not a regular on these forums so excuse me for being repetitive if such ideas have been discussed before.
P.P.S. I know this thread may not be the right place to discuss this but if there is enough public interest around this then mods please free to fork this out as a separate thread if I am not reachable.