The way I see it, the abstraction could be interpreted as this: when the number of buy orders is higher than sell orders, it means that, beyond just raising prices, the factories need to increase production without increasing infrastructure, by either raising working hours, creating an extra shift, using subcontractors (for example, temporarily using the capacity of another factory) etc. In the opposite scenario, the industry will simply have to produce beneath their capacity, since stockpiling is not an option (and would be risky/expensive if this was real life). So there are no 100 units of tools being created or disappearing magically. We're dealing with flexible production capacities, so the production in the game will always meet the demand (inside of a range). I agree that the lack of a stockpile requires a strong suspension of disbelief. But we have to keep in mind that in real life creating a huge stockpile is avoided by the industry, because it's a stagnant asset that only generates costs.