I believe in even competition and supply and demand.
The current system is, while romantic, heavily prejudiced against newer players as has already been mentioned.
One way to keep the “romantic” feel of the stalls could be that rather than having players rent the stalls, all stalls would be NPC operated. And players would register their goods at the stalls instead as the core mechanic. This would allow equal footing between players new and old, poor and rich.
The system could be further refined by filtering per stall and perhaps a master auctioneer in each settlement at which you could filter through all stalls, and get the stall location and number of your desired item.
To prevent the community becoming “lazy” and just registering everything at one specific stall for ease of use, you could have an item registration fee starting at free and going slowly higher and higher the more total items are registered in a specific stall.
This would ensure an even spread of items and also be a small “per player” based money sink since rich players probably won’t care too much with higher fees on stalls with large amounts of registered goods, while newer and poorer players would look for stalls with less goods to register their items more cheaply or perhaps even for free.
Just an idea
Edit:
And best of all, something like this shouldn’t be hard to implement either /hint hint devs
Edit 2:
To prevent the registration fee range to possibly get into silly numbers should a very high amount of items be registered in a stall, the fee range could simply have fixed tiers of fees. As such all that is needed to determine what a registration fee would be at a certain stall would be to internally have a list of all the stalls sorted by lowest to highest amount of items in each. At that point it is easy to assign fees to all the stalls depending on their stock, along with a minimum of x items in stall per fee tier to prevent an “empty” market to demand high fees.
It could be done in a whole lot of other ways that would work just fine as well