There are two general options for handling orders for which you wish to change the sale amount to $0:
a. Create customers for "Donations" or "Employees" or "Samples" and the like. Then create a sales order/delivery as for any other customer and as items are removed from inventory, they are "sold" through the sales process like any other item, only at $0. This method is ideal when trying to report on how much was given as donations, to employees, etc. You can have either one customer in your database labelled "Employees" or, if you wish to track it more specifically, can create a customer for each of your employees (or samples or those you donate to, etc).
b. "Goods Issue" can also be used as a means to physically remove the items without cost by pulling in the item code and changing the price to $0. You can then choose the variance on the drop down in the Goods Issue document itself to confirm whether it was a sample, employee liquor, donation, etc. This is more common for clients who don't wish to run reports regarding these sales and just want to remove them from inventory at $0.