Just a suggestion, but it would be neat to add essentially heat maps for some items.
For example, around Christmas time, there are all of the items that are needed for the cooking recipes like Small Eggs that shoot up in price drastically. I think it would be really cool to add this to some items, so that for example, if it was in high demand it would not be supplying at extremely low cost, and if there were sellers that were selling at higher prices (due to the high demand) the bot would still buy it (within acceptable limitations).
I think this would allow for market fluctuation, even if they are fabricated, and make it much more realistic. Now, you don't have to (and I am not suggesting that you should) get the data for every item in the game, but maybe get some for items that have commonly large fluctuations that are predictable, such as Small Eggs.