I think that it's a decent idea but requires refinement: Folks would only move their items to buy RS gold be at the top end of the 10%, there by pushing the average GE cost, wash and repeat and also the price of the thing on that day will probably bloat very sharply. If issue 1 is compared to wealthy players wait to sell on the day and will inventory pile items, since it is the price and an payout could be manipulated. I think that there needs to be a lockdown prior to it.
Perhaps a different mechanic may be used, such as the thing of the afternoon is worth 1.1X it's average GE worth in gold if you fall it directly in the pit. In that case it's 10% less expensive on average to throw the items in for the pet. I presume this would be abused that the. Could tackle it by not. There is zero reason for us understanding it other than to abuse that, so just do not tell us. I am sure some people may figure it out, but they'd be imagining, and they could also switch up the thing to 2-3 items rotating throughout the day or some number of alternatives to address individuals abusing it.
I meant more like when a product is chosen we'd know almost immediately, not beforehand (you might try to predict ahead of time but that might not be precise like you mentioned ). How I read the design of OP there will be a massive variety of the'item' after it is chosen, removed from the market. So this huge spike in item sells and/or related rapid shift from the supply/demand curve would be an alarm bell that is instantaneous. Any somewhat effectively trained algorithm would be able to decide on these sink items up (presuming they were really having an effect on the current market, which if they are not, then what's the point). With the method I am describing it would not be something that you could call beforehand but it could be something once it occurred, which you would know pretty fast.
More broadly, I'm simply pointing out that its very hard to'conceal' an artificial constraint (at least one which produces an important impact) on a marketplace if there's sufficient data available on the market. Demand curves and item costs are quite revealing on things like that. By using a list of items instead of one that are randomly chosen or jumped around like obfuscating, there could be workarounds. However, it would be an issue for OP's design if executed word.
Make it an occurance that occurs in the close of the gold ditch. If 10billion is tossed then this unknown item's correlating GE earnings are purchased out. No telling of it happening. No chance for abuse. Yeah thats not a bad thought. To minimize abuse potential even further I'd also suggest making the buyouts happen at random intervals, to stop people from just stockpiling random things and then posting them all at 9.9% over market place before the buyout happens. So then if the buyouts are random its still possible to do so, but you'd be sacrificing all of runescape 3 gold your GE slots to have items sitting there all the time so that it would be a bet.