Yes your “Misc” service item is exactly what I was trying to describe.
A popular till system used here in Australia (Vend) deals with negative stock like this.
The chashier scans all the customer items. When “Tinned Plums” are scanned an error message pops up telling the cashier that there is no stock and do they want to add it to the sale anyway. The cashier then has to click yes to continue or the sale will not proceed. Vend then just adjusts the stock level to -1.
If when a negative stock issue occurs in ERPNext would the solution above combined with adding a not in stock suffix (NIS) to “Tinned Plums” on the sale receipt be enough of a searchable flag to prevent fraud in your business?
When vend is offline a UI warning banner appears at the top of the screen making the cashier aware that the register cannot connect to the central DB. I imagine that stock numbers are loaded into Local Storage along with Item Name and Price etc.
Internet connections here in central Sydney (Australia’s most populated city) drops out at least once every 2 months. Yes I know thats crap. As such most ADSL 2+ modems now come with a 4G mobile network sim card for Fail Over situations.