My suggestion here is adding a market zone that would work like this:
There are, for example, 10 shopping spots, each one rentable for, let's say 20 yen, for an hour. People can only rent one spot per hour. In these spots, the one who rented 'em can place for sale things, such as weapons, fish, etc, for a price of his choice, without having to be there when people are buying. When the 1 hour rent expires, he gets all the benefits from the selling.