|Index||-||FAQ - Cart Help Buttons - Cart Settings - 8. Advanced Settings|
This option is off by default.
Normally the Field 3: itemcost (required) and Field 6: itemhandling (optional) are not allowed to have negative numbers. However, this option will allow negative values to be entered into these fields.
Note: If enabled, malicious customers may be able to use this feature to order products for free. For that reason it is recommended that you use this feature "Secure Product Information Using Inventory Control" if you are going to be using negative values.