Hi Michael,

I think there is no default way to achieve this.  You can go for out of box solution, achieve this by developing your own custom module.

Simple methods are:

• you can block sale if there is not enough quantity in hand(with reservation)

• you can disable the Force Availability function

Or you can: modify functions that affect stock quantity and check whether its going negative and if its, block it.

Here is a module for V8, you can check this, it adds function to 'stock.move' object to check whether after its done, is it going negative.

Here is another module for V7, you can refer this. They are using a constraint for 'stock.location' object to check whether stock quantity goes negative and blocks that.

Hope this helps.