I already suggested a ‘Billboard’ kinda system like this, listing shops, and their items, by owner. For Settlement Owners to place in their town somewhere, near the portals in and out of town.
But for the ‘Waypoint’ system, there is already a ‘System’ people can do for that. Namely, people can craft Location Tokens. Craft many of them inside the store, named after the store, then place them in a shopstand for 0g or 1g. And hope no one is an asshole and ‘Buys’ them all when you aren’t paying attention.
I can not see this being done well, because it relies on trust, with no punishment if the trust is broken. The two ways I see this being done is, through the Request Baskets, which A, requires the shop owner to FUND the basket with a budget. And B, the person ‘selling’ the resources, to not find some other store that is ‘buying’ resources at a higher price.
The second way is through trading, which can get very scammy very quickly. It relies too heavily on trust from both people, and if someone gets scammed, or the buyer/seller subtle makes the deal look good when it’s actually not, the other person can’t do anything about it.
You can’t ‘Hire’ someone for a job, where if they don’t do the job or destroy your stuff you can sue them and throw them in jail or punish some other way. If you befriend someone, and they don’t deliever, your out of luck. Or take advantage of your lack of knowledge on the prices everyone else is using to sell you a cheap resources for higher price, then again your just out of luck.
Creating a shop with someone else is a very very iffy situation, based very heavily on trust, and also on other factors. Like both people being Active, and working together, and liking each other, and playing at the same time most days.
It really doesn’t work out most of the time. We’ve SEEN that it doesn’t work out, most of the time. Most of the shops in the game are DEAD. Not 1, or 10, but MOST shops. You say you know 3 big shops, that’s THREE out of HUNDREDS of THOUSANDS of shops and players, across multiple worlds.
3 are the exception, not the rule. Just cause 3 are doing okish, doesn’t mean it’s right or normal, or even an ok system. After all, they are probably just a group of friends irl, or through other games, working together. Not everyone has a dedicated group to play a game with, especially not long term.