That’s trading, not a shop/market. The difference is that you don’t need to personally find someone interested in a trade, and can instead offer it to anyone that meets the requirements with less effort.
This was already an idea presented in a relatively old post about a new version of the trading system, Trading System v2.0 - Proposal. Specifically,
No market
Right now you need to trade with other users directly to gain items or DP from others. A market would allow users to open up for sale items to any user. The problem still is that this will suffer from the item problems mentioned above.