public double OrderItems(IItem item, uint amount) { ISupplier supplierForItem = Marketplace.GetInstance().FindSupplier(item); if (supplierForItem == null) { return(0.0); } if (_stock.ContainsKey(item)) { _stock[item] += amount; } else { _stock.Add(item, amount); } return(supplierForItem.Buy(item, amount)); }