The process of selling an item in the market is:

Click the "Sell" button in Buck Galore.

Click the "Create" tab.

The player will choose the item they want to sell.

Fill up the price and quantity.

Navigate to the "Current" tab.

I'm requesting a new button labeled "+" or "Add" next to the "Remove" button in the "Current" tab. This would allow players to easily restock their items without having to re-enter information.