How is that any different than messing with the prices?
You still haven't said why it would be back for the prices to vary. Or where I said it had to be automatic.
And varying the price - so that the first stall is cheap and the last stall is more expensive - is not even a fancy or un-thought of algorithm. It's literally what they do at Pike's Place Market. The more stalls are reserved, the higher the price will be to keep the stall. That market opened in 1907. This is the example I was thinking of.
When designing a game, you're playing with the very rules which encourage or discourage player actions. Taking or learning from examples in the real world - from markets to stadium seats' pricing - is one way of doing that without reinventing the wheel. And yet, many times you might have to. Economics is often called a very soft science because the very pool of actions will change depending on information and experience. An experienced pool will have very different reactions to a set of prices than an inexperienced pool of actors. So over time, both the buyers and the sellers have to shift their target around.
Which means literally that there is no one price; that 'right' price will vary; and it won't be just a matter of numbers to get the right price.
The number of vendors available on different days of the week will vary because the game does, in fact, have 'prime times' based upon the population of players. Trying to maximize and entice vendors to stick around and offer things is in itself a game for the devs to play. A game which has a 'right' answer that will never be exactly the same, as the players wil game right back at them.
And that's how economic incentives work!

