First, you need to go to Setup > Settings > Inventory Options. Once you are in the pop-up window select the Automatic setup of Sell Fast and Local Inventory option in order to enable it.

 Once this is done, go to Setup > Products and for each of the items that you want the system to automatically mark please do as follows:

• • Locate the product and under the Actions column click on Edit.
  • Set the number of aging days the system will require in order for a product to be marked with the "Sell Fast" icon.
  • Save your changes. 
    

Finally and keep in mind that this last step is optional, set the markup for the customers that will buy these items if needed. To do so, please follow the steps below:

• • Go to Setup > Customers, select the customer that you will like to set the price markup for and under the "Actions" column click on Edit.
  • In the top left corner click on Advanced.
  • Locate the Sell Fast Markup option on the right-hand side of the screen.
  • Set the markup amount either by percentage or dollar amount (positive or negative amounts can be used) and save your changes. Click on Save.